I agree there isn't much point in adding elaborate code to focus a system that is not repeatable, but at the same time there is a known issue with the current autofocus routine that could be a problem for sct users: It is hard-coded to take the curve from high numbers to low. If that happens to correspond to a clockwise motion of the focuser knob, then the curves will likely not be repeatable and focus will shift even after you stop, because when focusing an sct you want to push the mirror up against gravity.
I have focused very well using a variety of software including my own, on C11, EdgeHD8, and EdgeHD11 - and they all worked extremely well and were quite repeatable - as long as you provide enough backlash compensation and make sure the focus curve is taken with the knob turning counter-clockwise.
I have also had situations where the curves were not repeatable - and that was due to something slipping in the stepper focus system. So make sure nothing is slipping.
A good thing to do is place a mark on the focuser knob so you can watch it rotate - and make sure it is going the right direction, and that after going up and down and removing backlash - it still comes back to the exact same place. If the knob orientation itself is not repeatable, then the focusing of the mirror won't be, either.
I use about 1/2 turn of backlash compensation - which takes many seconds to unwind with robofocus.
When things are set up properly sct focusing with the knob works very well and there is no need to lose valuable backfocus by adding an additional focuser.
But if you find the autofocus curves turning the knob clockwise you will likely have a problem getting repeatable curves - and you may not be able to change settings with sgp or the focus driver to make it turn counter clockwise - because it is hard-coded in sgp. I had to rewire my stepper to make it go the right direction because of this limitation.
Frank