This looks to a very interesting housing. However, closer inspection and further research revealed a number of issues that would affect me.
There is no delete button, but that's not critical. More serious is the lack of a control to activate Macro focus. But perhaps the biggest drawback to me is the lack of any control of the Main dial on the Canon G5. This is the dial that is used to set aperture and shutter speed values in Manual Mode, Av mode and TV mode. You can select the modes, just not the values. I think this would make it difficult to shoot manual flash underwater. You could set up the values topside, but you'll have to keep them for the duration of your dive.
It should be possible to store a couple of setups in the CS1 and CS2 spaces on the G5, and these could be accessed via the Mode dial underwater. But again, you're limited to two combinations, with no way to adjust for conditions once underwater. These seem like fairly serious limitations to an otherwise nice housing.
I've made these observations based on looking at my Canon 5, and at the housing photos and information on the Aquatech web site. The nice folks at Backscatter.com could offer nothing beyond what was on the Aquatech web site. Please make any corrections if the above information is wrong.