This mouse is the best I've ever had. It beats the mx518 in almost every single way, albeit having almost exactly the same shape.

The round-ish shape of the mx518 makes it more resistant to shock than the angular protruded shape of the main buttons on this one. But that's about it.

I have small male hands and feel confortable with the whole button positioning. Have got nothing to complain about the software, either. For me this is the perfect FPS player mouse!

TL;DR at bottom of review.

BACKGROUND:

I have been an owner of the Logitech G9 mouse since 2009. I love that mouse so much that I bought a backup G9X when I found out they were no longer being made and panicked that I wouldn't be able to find a similar replacement when my G9 died (it still works great btw). I found this mouse after seeing some people mention it on the Logitech forums when it came out just a week or two ago.

I use a hybrid fingertip/clawgrip style which for all intents and purposes can be thought of as just a clawgrip. I have small hands for a man or medium size hands for a woman. The G9 was great for me as it was a small low profile mouse perfect for clawgrip. I used the "precision" grip as it was slightly more narrow and had a more grippy texture.

I do the typical everyday typical web browsing and Microsoft Office stuff. In addition to that, I play some FPS games and WoW.

G502 COMPARISON TO G9/G9X:
(G9 & G9X are the same mice with a better sensor on the G9X for those who don't know)

- Size/Form Factor - Slightly more narrow than the G9. Side grip points are rubbery and feels great to grab on to. It is taller than the G9, but not enough to make a difference for my grip style. It is also technically longer than the G9, but most the extra length is due to the longer main 2 left/right mouse buttons. This ends up also making no difference on my clawgrip style because I am still able to click those 2 main mouse buttons closer to the palmrest side of the mouse. Larger hands can click them farther away from the palmrest. I feel like I can grab on to the mouse with my grip style and really have control over it. Overall, I actually like the ergonomics of the G502 better than the G9 (never thought I'd be saying that!)

- Weight - I played around with the G502's included weights and ended up liking the weight of the g502 naked. Logitech's website lists G502 at 168g, and the G9 at 153g with precision grip. With the G9, I had 4x4g in the tray for a total weight of 169g. So I ended up liking about the same weight 168 vs. 169g. Ha!...who knew we could discern mouse weights so well? The G502 comes with an additional 5 x 3.6g weights, so the range is 168-186g. G9's range is 153-181g with the precision grip. If you like to use G9 without weights (or less than 4x4g put in), you will find the G502 a little heavier.

- Buttons - You get 11 programmable buttons with the G502 vs 9 programmable buttons with the G9. The 2 additional buttons are defaulted to "DPI shift" located at the tip of where your thumb lies, and the "profile switch" button located south of the mouse wheel. 2 standard thumb buttons feel better in that they are "clickier" and located more naturally for my thumb to hit when compared to the G9. The 2 DPI up/down buttons are moved to left of the left mouse button. DPI up ends up farther away north on the mouse which may make it more difficult to get to for clawgrippers.

- Mousewheel - Bigger and made of a sort of metal. I prefer the rubbery texture of the G9's mouse wheel better. The metal texture of the G502 almost makes it feel slippery at times, but the groves on the wheel itself, and the reassuring clicking make me feel confident while scrolling. Switch to go free scrolling is now located on the front of the mouse just south of the mousewheel which is much better (and makes it used more) as I don't have to look down and turn over the mouse to switch modes. 3 mousewheel buttons easier to click than the G9. Middle mouse button still stiffer than I'd like but much improved over the G9. This makes the G502's middle mouse button actually usable for me.

- Sensor - Obviously mouse sensor technology has gone beyond what 99.99% of people will ever use. G502's sensor is amazing. DPI goes up to 12,000, but I only use 2500. The sensor does feel precise and I don't notice any acceleration. Other people have tested this and note zero acceleration. I use a Steelseries cloth mousepad, and you can tune the g502 to different surfaces with the software...don't know how much of a difference "tuning" really makes in real world application.

- Miscellaneous/Software - Uses standard Logitech Gaming Software which works well, and nothing new to learn. Tried to use and tune it on my glass table which didn't work (Logitech does not claim that it will work on glass). Blue G light on palmrest can be turned off if too bright for user as mentioned in another review, but I personally like it and don't find it distracting.

FINAL THOUGHTS:

Logitech has made, in my eyes, a successor to the G9/G9X...not only that, but the G502 is a WORTHY successor to the G9/G9X. Logitech does not market the G502 as the successor to the G9/G9X, but the form factor, weight tuning, buttons, mousewheel, and sensor all certainly have the feel of the G9/G9X. The thing I wanted most with my G9 were a few extra buttons for gaming. I get 3 extra buttons with the G502 (counting the middle mouse as an extra button as I could never use the G9's because it was so stiff). The form factor of the g502 is great for my small hands, and fingertip/clawgrip style. Again, I think it would be great for larger hands as well due to the longer main left/right mouse buttons accommodating a range of hand sizes, but I'll defer that to other reviewers with larger hands. I am now officially using the G502 as my main mouse, and putting the G9 (and an unused backup G9X) in storage. Sort of sad to put away 2 excellent and working mice like that, but the G502 is an upgrade.

I tried to be thorough in my comparison, but I'm sure I forgot to mention things people are interested in hearing about so feel free to ask comment and ask questions.

TL;DR - Form factor great for range of hand sizes and claw grip. Shares many design principles (with many improvements, although some not as good ideas) with the old G9/G9X. I am replacing my G9 with the G502 and consider the G502 a worthy successor/upgrade to the G9/G9X.

Before you go too far, I absolutely hated the scroll wheel on this and wanted to return it. I did not realize there was an unlocked and locked setting for it, and unlocked and free wheeling, it will do all kinds of craziness when trying to use it for web browsing and gaming. However, I went back to the site with the intent to return it, and read the description that it's adjustable. After 3 days of "dealing with it" unlocked and losing my mind, I figured out the button on the top adjusts the scroll wheel sensitivity.

Beyond that, solid gaming mouse. This I feel like is the first gaming mouse I've ever purchased (and I've spent tons of computer mice and typically the scroll wheels always die) where the side and extra buttons actually feel intuitive and easy to use. I haven't actually spent the time programming them yet to games as I'm so used to not having them, but I really like the feel of this mouse and the placement of the buttons far more than any mouse I've bought.

I think the most immediately relevant thing to most gamers when it comes to this device is its weight. Its pretty heavy, and if you don't like that, or if your hand/wrist gets fatigued easily, you should consider other options. If you like heavy mice, well it even has additional weights that can be installed in the bottom very easily, but the amount of weights, and their total mass is much less than the g500's. All of the buttons are easy to press and are satisfyingly clicky, with except of one of the thumb buttons, which sits too far away to comfortably use without altering my grip, and the button in the middle of the top of the mouse, which I don't think is easily accessed with any reasonable grip at all. Logitech's gaming software allows for a great amount of customization, multiple profiles, as well as the ability to activate certain profiles when a certain application or game is running.
One other thing to note is that this mouse was almost impossible to clean when it got covered in "gamer gunk", so if you are susceptible to that, know that it will be incredibly difficult to clean.