S Tec 55x
I have been operating a Cessna 210 Turbine conversion fitted with the 55X A/P in conjunction with a Chelton Flightlogic EFIS system.
The A/P works well and is smooth in operation on this aircraft.
Mode selection operations are not particularly pilot friendly. but quickly become 'second nature' with experience
The Pre -Flight checklist is indeed long but we only carry it out on the first flight of the day. More than that and you will check it to death!