I used to own an S2a and the EC. The earlier Bronica cameras used a focal plane shutter. With the SQ, Bronica copied the Hasselblad and used leaf shutter lenses.
The fit and finish of the Bronica isn't quite as nice as the Blad but is a lot less expensive. The lenses are comparable in real life shooting. If you saw a bunch of 11x14's mixed on a table made with the Bronica and the Blad, you wouldn't know what was shot with which camera. The only negative that I have ever heard about them is that the film backs are the weak part of the system as far as reliability. Now you need to understand that I read this on the internet and I don't really know how true this is. Of course as cheap as they are, you can afford to replace the film backs if they wear out.
Koh's Camera in New York are the experts in Bronica cameras. In my experience, Jimmy Koh is a great guy to deal with. If you have any technical questions you can contact them.