an iFly newbie here (just registered and looking around)...
If the system works similar to the way the Garmin x96 handhelds worked, it's reading the turn not the bank directly. When I had a 396, I used to fly approaches partial panel using it and my saefty pilot friend was always amazed.at how accurately I flew. The key was (1) no sudden movements, everything always smooth and (2) realizing it was primarily for situational awareness. In my case I was helped more by the "DG" capability to help with heading selection than the artifical "turn coordiinator."
I would have felt comfortable using it in an emergency that way.