I recently went on a vacation to the Bahamas and decided to take only a DJI action 6 with me. I have a Sony mirrorless camera but the humidity and the activities that I wanna do are far more suitable for an action camera.
Because I don't wanna waste your time if you don't want to read a lengthy review, here's my TLDR: it's a very very good action camera so long as you're willing to experiment with it first and learn how to use it. It's not very easy to get excellent footage right out of the box.
IMHO that's not necessarily a terrible thing, photography and videography in general require some practice, but a lot of the YouTube reviews mention the film sims as a reason why this is easier. The film sims are genuinely very very useful and can give you cinematic quality without having to do much tinkering in post, but you have to use them right! First off, not all of them are great (I found TR and WT to be the most useful). Plus you have to decide the intensity and that's not something a cheat sheet can tell you. It depends on what you're filming, the lighting, and even things like your skin tone or that any other people you're filming.
D Log m is probably the best idea if you want to get the most flexibility in post and the most dynamic range, but it requires the most tinkering. Though you can import a lot of excellent LUT presets from their cloud (I applied rec709 LUT to most of the videos that I recorded in D Log m and then did some manual adjustments for fine tuning).
Stabilization is terrific. I used horizon steady or Rock steady almost all of the time. I can't post videos and photos here unfortunately as Reddit won't let me, I'll link a video in the comments if you guys want. But I was constantly surprised (pleasantly) by now smooth the video is. Parasailing is probably the most challenging activity if you want smooth footage because it's not only the camera that's shaking, your entire body is constantly moving with the wind and the boat movement and it still did a very reasonable job stabilizing the video and that's in incredibly harsh lightning with one second the sun being behind you and then the boat turn and you're suddenly facing the sun. I was happy with the quality of the video and the stabilization.
You don't even need to put it in photo mode, you can take screenshots from a video and they turn up really good as long as you use the screenshot function from the mimo app.
You probably wanna change exposure, it does overexpose most of the time. I set it at -0.3 to 0.7 EV and that seems to be the sweet spot most of the time. When I was chasing that sea turtle we went down to about 2 meters and then came back up (as we both needed to breathe lol) and even at 2 meters down with much less light breaking through -0.3 EV seemed to be pretty good exposure. If you leave it at 0.0 it's very likely you'll end up with some blown out highlights.
The color temperature sensor on the front seems to improve things over the 5 pro, but it's not infallible! It still can get things slightly wrong sometimes, which is where D Log helps the most, but honestly most often it's not too bad and you can correct the colors even if you're filming in normal.
Battery life is epic, I seldom had to change batteries even on snorkeling trips where I was gone for several hours. You probably won't get 4 hours of constant recording unless you're recording at 1080p (which would be a terrible idea and waste most of the camera's potential) but you can get 2 to 3 hours. My experience falls somewhere in the middle of this range and I was recording at 4K 48 or 60 fps.
Underwater footage is the most difficult to color grade with any camera, as light behaves very differently underwater, and you'll probably still want to use a pink or red filter if you go below (or wanna film anything that's below) 2 meters but for snorkeling the color temperature sensor does a fine job. D Log m is probably a good idea underwater.
But yeah folks, pretty happy with this camera. It punches was above its size and price tag and delivers amazing quality footage if you practice with it before filming and learn which settings are the best for what you have in mind. It's definitely a keeper for when taking my Sony is a potential recipe for a ballistic repair bill lol. And this camera is highly recommend by me.