**UPDATES BELOW, with some more Pros and Cons.

Original review:
I’m 7 days into the Sapphire Fenix 5 coming from a first edition Apple Watch. Needless to say, I upgraded my analytics game. What an amazing piece of equipment. Very much appreciate the accurate insights, exercise effects, VO2 Max, Functional Threshold Power, anaerobic fitness levels, you name it. This watch tells you exactly what you are doing and can do. And the fact that after 7 days of use with numerous 90 minute exercises, the battery level is still on 20%. Great. For me that's such a welcome improvement over the Apple Watch.

PROS
1. Multisport insights, accurate measurements; pace accuracy is fabulous
2. Countless features and functions
3. 100M waterproof
4. Rugged, beautiful design, looks great on wrist
5. Screen readable under direct sunlight
6. Long battery life (>week)
7. Sync to Connect app is seamless (wifi, bluetooth)
8. Comes with black and yellow straps, easily changeable
9. Its pretty light weight if you ask me
10. Oh, in case you're wondering; all notifications you'd come to love from the apple watch, are on here too. I can even control my music like before. No song searching or voice control though.

CONS
1. Software froze on me once this week
2. Screen was marketed as HiRes, don't really notice that though
3. Colors are a bit bland

All in all a great watch, very happy with it. Full recommend it to anyone who trains a lot. Especially someone looking to upgrade from an AW. Good luck with your choice.

UPDATE, April 20:
On to four weeks with the Sapphire Fenix 5. Watch has become inseparable from my daily activities. Really grown on me. More so than the AW had. I keep looking at it, its stunning black rugged design with capabilities that surpass expectations. Anyone on the fence, go for it. You wont be dissappointed. Do have some small gropes which are more related to learning curve I guess.

PROS:
*Only had to charge it twice this month (thank you!). Used it swimming, cycling, running, walking, strength training.
*I live high-up (8400ft) and the altimeter is spot on, barometer and compass as well. Unit takes the temperature from your surroundings, for example in the sauna you'll get accurate spikes.
*Must say the HRM is also better than expected which produces excellent data analysis on the watch and on the Garmin Connect App (also online). Does need to sit snug on the wrist, if not you lose accuracy. For example, on my daily 8mile bike ride to the office my HR stays in warm-up even though I'm sweating. Pulling the watchband tighter fixes the "issue". Related to using optical sensors, they say.
*If you want more data from running, an ANT+ connected HRM strap gives you access to additional menu for running dynamics, with real time info like cadence, ground contact time, stride length, vertical oscillation. Marvelous.
*Connectivity to more sensors. Im getting the HRM Swim Strap as well.
*BETTER ACCURACY, MORE DATA. Gotta love how Garmin feeds the need.
*Big fan of Segments. Race on commute segments against strangers. Strava also works wonders. Integrates well with online Garmin Connect.
*QuickFit wristbands in more colors.The black one I use while at work. The yellow one is good for the weekend. Looking forward to the leather strap.

CONS:
*First week the software froze, happened once more. So twice in a month. Restart is fast but does delete last 4 hours of HR data.
*Error in software sync pushes your morning alarms from app to watch but not vice versa. This means the alarms you configure on the watch get deleted upon sync with Connect app. Sure this will get a fix, is a bit annoying nevertheless (using iOS).
*Connect IQ apps. Well, coming from AW and its apps Connect IQ makes you feel a bit underwhelmed. Im sure I'll get into it. I wish I could find a better way to use the Navigate app. Learning curve.
*That said, downloaded Garmin BaseCamp to find courses and waypoints to upload to the watch but I was like, nope - I'll save that for later.
*Sometimes the watch kinda renews the connection with my iphone and I get double notified of emails, chats, calendar alerts.

Hope this helps. Have to say that after four weeks I still feel that I haven't discovered half of what the watch can do. Makes me a very satisfied F5 owner. I'll update again once I get the HRM Swim Strap. Good luck with your choice!

UPDATE June 1st:
I'll try to keep this short as its becoming quite a long read. Received the HRM Tri and Swim straps two weeks ago. Wanted to test things out before posting any comments. The HRM straps themselves are excellent, I use the Swim strap in a pool 3 times a week, the Tri I use for running and cycling. Both are very comfortable to fit the purpose of long runs or swim sessions. *I do not live close to open water. Once you get your first access to the extended data such as Running Dynamics and swimming Swolf, you'll be amazed. Especially if you're a first timer like I am. What you cant help thinking though, is that the heart rate data quality becomes so much better with the straps that the optical wrist based data is bound to disappoint afterwards.

PROS
Heart rate real time data a LOT better, changes in heart rate are visible instantly
Running dynamics help you improve your balance and running style* (this is quite a considerable change, actually)
*even on a treadmill.
Pool swimming data is fabulous, not as extensive as Running Dynamics. I attached new Garmin Connect screen shots.
Additional Lactate Threshold and HRV Stress tests are now available
Overall additional datasets make you feel you're entering a professional training environment

CONS
Optical wrist based heart rate accuracy does disappoint, but I doubt it would have been noticeable without acquiring the straps? Not sure.
Swimming heart rate is not available under water, the unit will download HR data after you finish your exercise. This works flawless so no problem at all.

For what its worth, I'm really happy with the straps and additional training data. The graphs are great, the insights in your performance gets better and better. It is quite an expensive combo if you go full fenix5 + straps. Agreed. But I'm using this equipment every day, so I tell myself its money well spent. If you have any questions, by all means. Good luck and stay safe.

At first, I felt overwhelmed that I spent this much money on this. The first couple of days were spent feeling guilty and ashamed, but man I love this thing. I have the white, champagne sapphire 5s. I am uploading a photo for any women out there interested in this. I have tiny hands and a tiny wrist so you can get an idea how it looks on the smallest of wrists. This version comes with the gray suede and the white strap so don't buy the additional strap that it says "frequently bought with" The battery life is amazing. I charged it 2 days ago, ran twice since then and I'm at 76% The champagne worried me because I was afraid it would look too much like yellow gold since I'm a white gold and sterling silver person. It's not gold at all. it's very subtle. The white is very feminine and pretty. I am glad I didn't go with the black.

2 more runs and a hike and I'm now at 52%. Love the battery life.

This review has been updated and its rating increased from 3 to 4+ stars since Garmin Fenix 5 software upgrades have improved Altimeter accuracy (see TIPS section below for accuracy improvement settings).

While I use my Fenix 5/S for all sorts of things, this review is predominately from the perspective of the hike/climb activities. I have no association with Garmin or any other seller. I use the Fenix 5/5S to track half-day and full-day activities. Activities include on/off-trail hikes with steep mountain ascent/descents, with/without trekking poles. Climbing in mountainous terrain can present unique accuracy issues, especially for Altimeter, Ascent/Descent, and Step-Count metrics. See the TIPS section at the end of this review for ways to improve the accuracy of these metrics.

---------- BACKGROUND ----------
This is the fifth Garmin wearable device I've used (my first 3 were FR610s, my forth F5, and fifth F5S). I was originally going to purchase a Fenix 5 (F5) when someone who was having accuracy issues asked me if I would like to try it out. While I liked the F5, my thinking evolved as follows:
1) I noticed May-June F5 devices had un-explainable Altimeter accuracy issues.
2) I knew historically Garmin software updates have addressed accuracy issues.
3) I felt the F5 47mm was too big for me (8" wrist) which excluded F5 and the F5X.
4) Fenix 5 devices come in 3 models: 42mm F5S, 47mm F5, and 51mm F5X.
5) I originally excluded the Fenix 5S as a women's watch due to colors shown.
6) After reading reviews, I realized Fenix 5S does everything the Fenix F5 does.
7) As a result, I found the Garmin Fenix 5S a welcome alternative to the F5/F5X.
8) In June 2017 I ordered a black/black Fenix 5S (42mm) with Sapphire option.
I picked the Sapphire option not so much for the crystal, but for direct WiFi connectivity and fast upload associated with the sapphire option. While the sapphire crystal is nice to have, I still purchased tempered glass screen protectors which I strongly recommend for hike/climb activities because these are "contact sports" with rock. The screen protectors for the F5S fit great. You cannot tell they're installed unless you bash your watch into a rock while climbing and the protector saves the watch face from being scratched.

---------- IMPRESSIONS AFTER 1 DAY ----------
My first impression of Garmin Fenix 5 devices is that they are precision made, especially in comparison to many other GPS watches. The buttons on the Garmin Fenix 5/S/X have a very high-quality look and feel. Within 15 minutes of setup, I found the watch friendly and easy-to-navigate. That's coming from someone who has only used touch screen devices until now. Button functions seemed logical and rugged with advanced features such as programmable hot-key/long-press button re-assignment.

I quickly learned how to customize the display of altimeter, elapsed time, distance, lap, heart-rate, sunrise-sunset, moon rise/set/phase, and GPS info. These are all useful features for mountain wilderness climbing activity. Out of the box these watches allow customization of up to 4 fields per screen. For example, for hiking in mountainous terrain I setup one screen with: Elapsed Time, Distance, Elevation, and Heart-Rate. You can also add multiple-screens to an activity, so I added a GPS screen to show GPS signal strength, longitude, latitude, and elevation; I also added a screen with current time, sunrise, sunset and elapsed time so I can be aware of how much daylight or night time I have left during an activity. You can also add more customized screens to an activity if needed. There are also add-on screens/data-fields that allow many more fields per screen (if desired, but I found I didn't need these).

---------- IMPRESSIONS AFTER 60 DAYS ----------
I initially encountered accuracy issues with Altitude, Ascent, Descent, Heart-rate, and Distance metrics. After the first month, I'd found partial solutions for some accuracy issues (see TIPS section below for detailed info). After 30 days, I liked my F5S enough to keep it. I had initially considered returning the device because I was unhappy with Altimeter and Heart-Rate accuracy. After 60 days I still liked the watch, but was disappointed with Altimeter inaccuracy.

For the first 3 months, my Fenix 5 altimeter was off by up to 150 feet per 1000 foot gain. But after the Garmin software update in October 2017, Altimeter accuracy became greatly improved. Altimeter error was reduced from 15% error down to less than 2% elevation error. My daily workout involves an activity with known elevations. Thus my altimeter accuracy analysis is based on waypoints with known elevations compared to the amount of elevation error observed per 1000 feet ascent/descent. Before the October update, the elevation error per 1000 foot of vertical climb was accurate to only within 150 feet (15%). After that Garmin software update, the altimeter was accurate to within 20 feet per 1000 feet (2%). That's a BIG improvement. I now feel the Fenix 5 is an awesome watch for Hike/Climb activities (see TIPS section below for settings used to achieve this accuracy level).

After 60 days I was also surprised by many features present in the Fenix 5 devices that I was not expecting. For example, I was not expecting FENIX F5 watches to be "smart" watches in the sense that they could display: text messages, email, and calendar notifications. The watch also includes a widget to display your mobile device's music track name and artist automatically. In addition to that, the Music widget lets you control Volume, Pause, Play, and Skip music on your paired mobile device. I was also surprised I could control the Spotify app on my mobile device from my Fenix F5 device. To be clear, you can use your F5 watch to control Spotify on your mobile device. What was most surprising, you can control the Spotify Desktop for Windows from your F5 device via your paired mobile device. Thus, you can control a whole home sound system's Volume, Pause, Play, and Skip music. These features were not something I was expecting, nor was I looking for them, but now that I have them on my wrist, I find that I use.

Another pleasant surprise was Garmin Connect IQ (which is the Garmin app store). Connect IQ includes many useful additional apps, widgets, watch-faces. For example, there's a Weather Underground widget that lets your obtain localized Temperature, Wind, Humidity, Precipitation for the closest WU weather station near you. The WU Weather widget is especially useful for those of you who adventure in remote areas, since the standard Weather Connect IQ app from Garmin only provides weather information for major cities (which is not useful in mountain wilderness areas). In contrast, the WU widget lets you assign a "home" weather station. With over 100,000 weather stations in the WU database, that means you can obtain localized weather info such as Wind, Temp, Humidity, and Precipitation for your local hike activity.

Battery life is also much improved over older Garmin wearable devices such as the FR610 which could only GPS track for about 5-6 hours before the battery was dead. In contrast my Garmin F5S on its first 9 hour climb used less than half the battery (with HR turned off). Thus, you can GPS track 2 day treks on a single charge on the 5S, and 3 half-day treks on a single charge (I turn OFF the wrist Heart Rate monitor except during steep ascents to conserve battery... no point burning wrist LEDs to monitor hours of level/downhill HR).

---------- IMPRESSIONS AFTER 120 DAYS ----------
Altimeter accuracy errors were fixed with Garmin Fenix 5S October 2017 software updates. As mentioned above, my altimeter accuracy per 1000 foot is now within 2% (within 20 feet per 1000 foot gain, and often is within 10 feet). Given these improvements in altimeter accuracy, I now use my Fenix 5S for all hike/climb activities, and have become a Fenix 5/S fan. Through software updates, the Garmin Fenix 5S became the high-quality high-precision activity tracking device I hoped it would be.

I have noticed there are still several Amazon reviews that state they have Fenix F5 or F5X altimeter accuracy problems. Hopefully this is a case of folks not updating their firmware and/or their reviews, rather than defective devices. Or could altimeter accuracy be due to differences between different Fenix 5 models? If recent Garmin software updates did not fix altimeter issues on your F5/F5X device, please comment below. I'm considering purchase of a second backup Fenix 5 device, but cannot decide whether I should consider a F5, F5S, or F5X due to concerns about this altimeter issue with different models.

---------- PROS ----------
1. Built-in heart-rate accuracy improved (was inaccurate until I used Tips below)
2. WiFi with Sapphire (WiFi allows fast SAVE of activity without mobile phone/wires)
3. Mobile Connect interface seamless (allows up/download of data, apps, widgets)
4. Decent Battery Life (can do multiple/day-long GPS activities on single charge)
5. Custom screens: Elapsed-Time, Distance, Elevation, Heart-Rate, GPS, Sunrise/set
6. Custom activities and fields allow extreme customization of data fields/screens.
7. Copy/Create activity allows Copy HIKE, Create HIKE2 with different metrics/screens.
8. Custom watch faces allow extreme customization (e.g. Hands Five dial watch face)
9. Text, Email, Calendar Notifications display on watch, with easy read/delete functions.
10. Music app controls Volume, Pause, Play, Skip; even works with Spotify for PC.
11. Up-to-speed quickly with easy-to-learn, intuitive user-interface.

--------- CONS ----------
1. Wrist Heart-Rate monitor not always accurate (see Heart Rate Tips below).
2. Altimeter/Ascent had 10-15% error out-of-the-box (see Altimeter Tips below).
3. GPS setting caused inaccurate Distance metric (see GPS Tips below).
4. Step-Count is inaccurate with hike/trek poles (see Step-Count Tips below)

---------- TIPS ----------

1. HEART-RATE monitor is not accurate unless the watch band is VERY tight. If you find this bothersome, or cannot obtain accurate readings, use a chest strap instead for accurate heart rate info. As someone who has used a heart rate strap for 5+ years, I like the freedom of a wrist heart-rate monitor, especially since I only use heart-rate during steep ascents to avoid overreaching my HR. I especially like not having to wear a chest strap while climbing. I turn OFF the wrist heart-rate monitor while not climbing during long activities to:
a) Reduce Battery drain from illuminated wrist LEDs.
b) Not track low effort heart-rate activities during long hikes in/out of climb.

2. ALTIMETER and Ascent/Descent metrics had accuracy issues out-of-the-box, especially in mountain terrain. The watch consistently under estimated Altimeter/Ascent metrics by 10-15% while hiking steep terrain. For example, a known 2000' ascent instead showed as being a 1700-1800 foot ascent. I discovered the cause for this: a) Fenix 5 software needed updating, and b) the Fenix 5 watch by default uses the AUTO setting for the built-in Barometer to determine elevation changes during the hiking activity. Fenix watches have a setting that allows you to indicate whether pressure changes are due to weather conditions or due to elevation changes. The default AUTO setting for the Fenix watch allows the watch to potentially incorrectly attribute barometric pressure changes to changing weather conditions rather than to elevation changes while climbing. When climbing in steep terrain, the AUTO setting consistently resulted in underestimation of pressure changes due to elevation changes. You can eliminate these types of elevation ascent/descent accuracy issues by changing the Barometer Watch Mode setting from AUTO to ALTIMETER with the following steps:
a) Long Press Up/Menu button.
b) Scroll and select Settings
c) Scroll and select Sensors
d) Scroll and select Barometer
e) Scroll and select Watch Mode
f) Scroll and select ALTIMETER
Once you do this, you should also re-calibrate the altimeter at the start of a climb regardless of the barometer setting. Thus at the beginning of each hike scroll to the Altimeter Widget, select Calibrate, and either Enter Current Elevation, or Use GPS so you start with the correct elevation. It is always better to calibrate using known elevation, rather than use GPS, since Garmin advises that GPS derived elevations can be off by hundreds of feet (although from my experience hiking/climbing in the Colorado Rockies, the GPS elevation is usually accurate to within 50 feet). For more about this subject you can Google "Troubleshooting Fenix 5 barometer".

3. GPS and DATA RECORDING settings can cause Distance accuracy issues when hiking in mountainous terrain. I almost returned my Fenix because I kept getting wildly inaccurate distance metrics when the GPS setting was set either to ULTRATRAC or to GPS. Distances were consistently 10-20% lower than the actual distance when GPS was set to UltraTrac when hiking is mountainous terrain. Distances were wildly and erratically higher when GPS was set to GPS instead of GPS+GLONASS, with distance metrics off by as much as 50% (e.g. a known 8.5 mile hike kept coming up as 12.5 miles).

How to set HIKE Settings for GPS to GPS+GLONASS instead of GPS or UltraTrac:
a) Long Press Up/Menu button.
b) Scroll and select Settings
c) Scroll and select Activities
d) Scroll and select Hike
e) Scroll and select Hike Settings
f) Scroll and select GPS+GLONASS.

How to set DATA RECORDING to Every Second to avoid inaccurate tracking:
g) Repeatedly press Back button to return to main screen.
h) Long Press Up/Menu button.
i) Scroll and select Settings
j) Scroll and select System
k) Scroll and select Data Recording
l) Set to Every second.

4. STEP-COUNT metric can be inaccurate when hiking in steep terrain and/or with trekking/hiking poles. People who hike/climb in steep mountain terrain often use trekking/hiking poles to reduce odds of slipping/falling on scree, talus, boulder-fields, snow, ice, etc.
As a result, step count can be low due to:
A) Hiking with poles makes arms stationary for duration of pole plant (3-5 steps instead of 2).
B) Hiking in steep terrain and slowly selecting pole placement results in little/no arm motion.
C) If hiking steeps with poles, actual step-count is 1.5 to 2.5 times more than reported by F5.
D) Even without poles, hiking/climbing causes use of hands to steady oneself, resulting in inaccurate step-count since it relies on arm motion.

Step count assumes you take 2 steps per arm swing, but when hiking in steep terrain actual steps per pole plant are from 3 to 5 steps instead of 2, thus step count reported by F5 is much lower than your actual step count. If you are steadying yourself with poles or climbing with hands on rocks, there is less arm motion for more steps, thus step count reads low. Step count for trekking pole hikers would be greatly improved if Garmin provided an external sensor for step count. Unfortunately, the Garmin Foot Pod accessory does not update the step count metric, but rather provides an alternative distance metric, and only if GPS is unavailable (e.g. when on a treadmill or indoor track). Readers, please comment if you know of an accessory that attaches to the foot and provides an accurate step count for F5 devices as an alternative to wrist-arm movement step count.

2017/11/8 – Updated review, corrected grammar, changed rating from 3 to 4+ stars due to greatly improved Altimeter accuracy. Why not 5 stars? I still occasionally experience a GPS track issue that causes a wild GPS track in valleys (I will upgrade rating when/if the issue is resolved).