I purchased the EVO GP-PRO 3 Axis GoPro Gimbal for Hero4 with 3.5mm AV Output, 4-Way Joystick, Multiple Operating Modes, Built From Aircraft Grade CNC Aluminum for a vacation before the Karma Grip was available, and ended up returning it and buying the Karma Grip at a local store instead. I found the Karma Grip to be a much easier to use and more integrated package, plus it has usable audio and is much cheaper than the EVO GP-PRO. There are definitely trade-offs between the two devices, so think about how you're really going to use a gimbal and what you want from it before you make your decision. I'll compare their pros and cons below.

GoPro Karma Grip
Pros:
* Good video stabilization
* Very minimal noise from the gimbal motors. There is still some sound that is picked up in the video, but I consider it an acceptable amount, and I am comfortable using audio from the camera when it is in the gimbal.
* Quick release frame so you can put in or take out the camera with the flip of one little latch.
* Can power on the gimbal and camera at the same time with one button press.
* Can start or stop recording with a button on the gimbal. This is very handy. For instance I used it on a bike ride, holding it one-handed. I could start and stop recording with one hand easily. That wouldn't be possible with the GP-PRO unless you got the voice commands working with the horrible audio, or had a remote taped to the gimbal handle.
* Can insert highlight points into the video from the gimbal handle.
* Greater control over panning the camera up and down. Instead of a joystick, you hold a button on the gimbal handle and then tilt the handle up or down. I found that this gave me greater control of speed and precision than the small joystick on the GP-PRO, though in some situations it may be impractical to make that tilting motion and the joystick would be better.
* Includes a nice soft-shell carrying case that stores the entire gimbal assembly with the camera mounted, and some room for other accessories as well.
* Significantly cheaper than the GP-PRO, plus it comes with the nice carrying case and doesn't require the purchase of extra adapters for use with the HERO5.
* Gimbal assembly can be removed from the handle and mounted onto a backpack mount, or any other mounts that come out in the future (will require additional purchases)
* Can be used with the Karma Drone, if they ever fix the issues with them and start selling them again.

Cons:
* Shorter battery life than the GP-PRO (~2 hours on the Karma Grip compared to 6+ hours on the GP-PRO from what I've read, though I haven't tested the limits of either myself)
* Can't swap the batteries, have to wait a long time for the batteries to recharge (I've read 6+ hours to recharge without the fast charger, though again I haven't tested this myself in any measurable way)
* The screen of the HERO5 is partially blocked by the back gimbal motor when you hold the handle vertically. I haven't had trouble still using the screen to frame up shots since it's not completely blocked, but it's something to be aware of.
* Ports on the camera are plugged into the gimbal, which allows the camera to control the camera, but also blocks the ports for use with something like an external mic.

EVO GP-PRO
Pros:
* Good video stabilization
* Long battery life
* Swappable batteries so you can bring an extra set for long trips and not have to recharge
* Several stabilized modes.
* Joystick to make the camera look up or down can be handy in some situations.
* Good build quality. Basically it's just an aluminum tube with some batteries in it and a couple of buttons.
* Can access the ports on the side of the camera when it's mounted in the gimbal, so you can plug in an external mic or remote if you want.

Cons:
* Completely unusable audio with HERO5, not sure about other models. I contacted the company and they basically said it's a known limitation (that they don't talk about in any of their marketing material before you pay $400 for their device) and that there isn't much you can do for it. They suggested switching the audio recording settings on the HERO5 to separate the audio from the three microphones and use the audio from the mic farthest away from the motor. Didn't work for me, still completely unusable.
* Had to buy another $20 adapter to make the HERO5 work with this. They are really gouging on this price, it's a very small piece of plastic and two screws, plus they charge for shipping! Considering I already bought their product, they should charge $5 with free shipping, at most. Ideally they would simply send it to customers that show proof of purchase after the HERO5 came out, considering the cost of the item to them is almost nothing.
* Have to unscrew two thumb-screws to remove the camera from the device, it's not a very fast or easy process if you frequently need to remove the camera.
* Have to turn the camera on and off separate from the gimbal. Just extra buttons to push. Also have to reach up and press record on the camera before or after the gimbal is turned on. Could be avoided with voice commands on the HERO5 or a remote I guess. Though with the unusable audio, the camera probably wouldn't even hear your command, I didn't try it.
* No carrying case included. The case they want to sell you is another $130, and it's a very large and bulky hard shell case. The box it comes in is nice enough for shipping, but it can't be used at all for storage or traveling, you have to completely break down the gimbal to put it back in the box.
* Gimbal assembly can't be removed from the handle.

Like I said, there are trade-offs for both gimbals. If you need to be able to shoot video all day, the GP-PRO is your choice because it has longer battery life and you can swap in some fully charged batteries easily. If you want ease-of-use, usable audio, and an integrated package, the Karma Grip wins for sure.

I found the quality of the video stabilization to be basically identical, so consider the other features, overall design of the product, the price, and your needs when you make the purchase.

Follow the advice found in other reviews here--check for and update the software in your GoPro hardware before you ever turn on your Karma.

-Superior stabilization--this transformed the quality of my GoPro footage both on foot and bike.
-Despite software updates there are still inexplicable shutdown issues. I've done factory resets in the field to get everything working again.
-Sometimes the red 'record' button on the Karma grip works. Sometimes I have to press 'record' on the Hero5 instead.
-User documentation looks like a budgetary afterthought. Get used to using search engines and video reviews for tips and troubleshooting.

To GoPro:

I want you to succeed with all of your products and I make a point of loyalty to exclusively purchase your marked-up accessories and components, but there isn't a reasonable excuse for rushing the Karma out without enhanced quality control at this price point. Like many consumers, I don't make investments on the scale of the Karma unless I'm prepping to document a significant family trip or expensive holiday excursion, and troubleshooting is NOT a product learning curve. You're not producing a video game--we're paying more than $60 to wait on a product for patches and fixes. You cannot afford this product release strategy in the future. Your rushed release of the buggy Karma is exactly why I won't consider adding the Drone Flight Kit to my GoPro inventory anytime soon.

I bought this very expensive piece of equipment to film a movie of an international vacation. The first 6 days the Karma Grip worked amazing and was worth every penny. It then started to connect to my GoPro Hero 5 Black slower and slower as each day passed. Two days later it says "USB connected" on the GoPro screen and will no longer connect. I looked online and there are thousands of cases where this has happened to owners. I tried every step that others have used (60 second restart, making sure firmware is updated, reformatting my SD card), and none of these worked. I now have a $300 piece of equipment that does not work at all. It also ruined my movie from a very expensive, once in a lifetime vacation. GoPro offered to exchange it since its within warranty, but how can anyone purchase this with confidence if it might break again after the warranty is up?

This product is just terrible. Seems to have a major issue known as "USB connected", that won't go away. It worked for one day, then started showing that message and unfortunately, it started with the issue once I was already in the Patagonia. I took this expensive piece of equipment just to waste space of my pack. Once I got back I called GoPro (terrible service btw), sent me a replacement harness and it didn't work.

Contacted Amazon, whom after 3 days had a replacement on my doorstep, and guess what? "USB connected". Again.

I've contacted Amazon again so I'm waiting for an answer on what to do. Very frustrated, as I had huge expectations... GoPro should've probably recalled this grip as well.

This thing works really well. Haven't had any issues with it and the stabilization is fantastic.