Wow! This is one of the coolest threads out there! I am very jealous of anyone who owns any of these machines! Thanks for putting such a good collection of photos and details, very interesting indeed.
My local tennis shop has a Sensor Expert and a pretty old one with a dial to enter tension (not sure what model, looks like a Star 3 I think) and they look super cool. Might be able to string on my clubs sensor dual at some point.