The Helicommand Rigid version is a flybarless system that unlike other flybarless systems offers an auto-stability mode(s). I have had this system on my 10s flybarless Trex600e for almost a year now and I really like it.
If you are using the internal HC tail gyro then I would avoid using the combined auto-trim/gyro function since you will still need to set your heading hold gains with your PC. This can be a real pain since the internal tail gyro is pretty sensitive to temp. changes and/or different aged battery flight packs.
If you are using an external tail gyro (I recommend you use one, even a Fut401 works much better than he internal one in my opinion) then you can assign your Aux2 to auto-trim and your tail gyro gain to say Aux3. That is what I'd do if I had an extra Tx/Rx channel (I only have a 7 channel DX7).
Personally I have not found any need to use the auto-trim Tx function. All I do to trim up the heli is first to trim it up in non-stabilisation mode, land and mechanically adjust the swash servo's until it hovers very level. I then put it into a level hover and switch on Horiz Mode (using HC Fixed). I don't use Position Mode (piece of black tape over the HC Position camera) so I have my pilot switch set to Up=0 (no stabilisation) and down=80% (gain in horiz mode). After about 10 sec (to let horiz mode to settle in) I may need to use one or two clicks of elev/ail trim to hold a nice level hover. After that, I just land, center the controls (including setting the collective pitch to full negative) and press and hold the HC set button for a few seconds to reset the auto-trim Tx neutral set-points). I then turn everything off, and zero out any elev or ail Tx trims and the next time I fly all's well.
Hope this helps Reg.
Good luck and Cheers,
Ion-x, 10s ,SS
TT X50E 10s, HC3-Sx