I shoot with the FS7 regularly for commercial work (non-underwater work, that is), and based on those experiences with the camera I feel confident that it would be at home in the water. The 10-bit color for internal recording should render clean gradients with no banding artifacts. It's a stellar camera image, as long as you can work around the slow menus and other setup annoyances.
I just purchased a 10m bag for the FS7 to use on a few January projects in shallow depths. I will likely shoot with the FS7's LC709-TypeA MLUT applied, or Slog3. At that depth, probably no need for a red filter.