The feature-set and price point of the DJI Osmo Action make it pretty obvious from the get-go that it's an attempt to undercut the GoPro HERO7. Does it succeed? Like all things, it's complicated. The front-facing screen is a boon, the stabilisation is just as silky smooth as the HERO's, and it's wallet-friendly price is nothing to sniff at. That's not to say it's perfect; there are a few lag issues at high resolutions, the app can be unreliable, and video from the HERO is a touch flatter, which counts in professional realm when it comes to the grade. For an affordable alternative to the HERO7 Black though, the Osmo Action is a fantastic choice.
Another highly sought-after, and relatively exclusive, feature within the video camera realm is the ability to record in RAW or ProRes. These are uncompressed formats that maximize the information gathered by the sensor and provide you with extended flexibility when it comes to color grading and post-processing. As mentioned, this feature is quite an exclusive one and only available in a select few cameras on the market with good processors (again, excluding high-end cinema systems). Some select cameras can record in ProRes Raw with an Atomos Ninja V external recorder. Nauticam offers a housing for the Ninja V for use with your underwater system.