It's my understanding that the STEC autopilots get their "bank"
information from the gyro in the turn coordinator while other systems
derive this from the vacuum-driven horizon indicator.

Are there any TSO'd systems other than STEC that do this? I ask the
question because STEC's new owners are preparing to milk this cow to
death by raising the system prices by 2 AMU, and some serious
competition would be welcome.

I consider the TC based system better because the TC is a much more
reliable instrument than the AHI.