I've been wanting to down size for a while and decided to go with the R50 about a month back. I bought the "Pro" housing package from BlueWater Photo and was really happy with the transaction.
I've not been diving with the unit yet, but I am really pleased with the housing / package. That said, I have a few nit picky comments. First, yes you can implement back button autofocus, BUT only as a reprogram on the "*" button (which is * / magnify button on the housing). I don't see where Canon provided the alternative on the other buttons (although there is a lot of other remapping available on the other buttons). I too found the trigger to have no "feel" to it and, if you reprogram the * / magnify you can't reach the reprogrammed button and trigger at the same time. My solution is to remove the add-on trigger. Once removed you can comfortably hold the back focus and click the shutter release. Removing the add-on trigger eliminates the soggy feel it gives and, with the reprogrammed button gives the desired function.
Another weird issue is the functionality of the housing AF/MF button. Yes, pressing it lets you switch from AF to MF, but there is no way to MF once you do this!! Nauticam did not externalize the manual focus ring on the lens. The knob labeled as Zoom/Focus is really just a zoom knob. I wrote Nauticam about this and they mentioned that the user manual will someday be corrected. Of course, all their other housings allow the alternatives based on one's gear selection, but no such option exists for this rig. As noted above, the AF/MF button has an extensive set of Canon alternative functions so I guess I'll eventually find something I want for the button.
The housing flash ON/OFF works beautifully and it's a nice feature. I was always wishing for an easy way to do this on my A7RV and never found it.
I'd be interested in knowing if anyone has a way to get to an effective 100mm (full frame) lens. The existing is effectively 76mm. For fish portraits I'd like a bit more telephoto. I already have the CMC-2, so I'm OK for getting in very close but, of course, you pay a DOF penalty when the CMC and similar are used.
Overall, seems like a nice alternative if you can manage the limitations.
Gary