Hi Olivier,
My current setup is a bit over 12 years old, so nearly prehistoric by digital standards, and it's not the Canon compact with the 3 flash settings. I'm trying to decide what to do for an upgrade, and the G7x ii has a lot going for it.
I don't expect to take advantage of the fast burst mode much for UW shooting, but I can imagine there may be times when I'd want to quickly fire off several shots in a row. My thinking is that I don't want the onboard flash recycling to limit shooting before the external strobes do. A hot shoe eliminates the onboard flash as a possible limitation, and better battery life is a bonus.
In case the G7x ii is different, mine shows a line divided into thirds, with a 13 segment bar graph underneath. The 3 power settings display 5, 9, and 13 segments, which implies something near the 1/3, 2/3 and full power settings I mentioned above. Like the manual focus display, they could display a real number that has meaning, but that idea seems to have eluded them. Since I just do casual stuff with it I've always just dialed in a flash power and f-stop that work, and never paid much attention. Of course once I started to actually think about it changes of a full stop make far more sense than 1/3, 2/3 and full power (and match just about every external flash I've ever owned). From what I've found Canon offers no documentation, but I took a few pictures to work it out. What I found was that the reduced power settings are roughly 1/2 and 1/16 of full power. Slightly odd choices for general usage (is it really that hard/expensive to add more intermediate levels?), but assuming the low power is enough to reliably trigger a slave via fiber optic that's a pretty good alternative to a hot shoe. The camera only takes about 1 shot per second, but I managed 20 shots in a row. I don't imagine I'll find performance like that to be a limitation in an UW setup.
