I agree that it would be nice for the STEC in my Glasair to do a
better job of flying the analog needle output. I have worked on the
sensitivity tailoring by hanging internal resistors under the
direction of the technical service personnel at STEC and can only get
it a little better than when I started. Also, tinkered with the roll
centering that is a user adjustment (hidden under a panel screw) to
try and null that out as best as possible. The Glasair just has too
much roll sensitivity to do a very good job with this particular
autopilot in NAV mode, but in roll steering mode where, yes, it is
"faked" into thinking it is in an everchanging HDG mode, it works
great.
I also agree with the poster that you can drive the autopilot any way
you want when doing an approach using terrestrial nav aids and as long
as you are watching the appropriate needles it is legal. One way is
to just put it in HDG mode and keep tweaking the heading bug. I guess
that is a "brain-driven" coupled approach. It doesn't matter where
the autopilot gets its intellengence from as long as the aircraft is
flying on the right path.