I haven't trained with them but I know two of the instructors there. THe Chief Pilot has a tremendous amount of instructing experience in GA aircraft to include the King Air 350. He has also flown several heavies and corporate jets so he has experience in a wide range of aircraft. The aircraft itself is in beautiful condition and they take great care of it over at KJYO.
I've met a couple of Avenge pilots who had nothing but positive things to say about Potomac. Hope this helps!