Thet are very nice cameras, incredibly rugged and equipped with great optics. You can use them with a variety of backs (Polaroid, Graflok or Mamiya for 120 or 220 roll-film in 6x4.5, 6x6, 6x7 or 6x9, sheet film, ground glass, etc.) and lenses (50 to 250mm). Their 2 main drawbacks are:
- bulk and weight, as the whole set (camera + back + lens) is quite big & heavy and its shape takes a lot of room in a camera bag;
- no idiot proofing of any kind: you are on your own to shoot nice pictures of the darkslide, double or blank exposures, to fog your film by removing the back or the lens without securing the darkslide, etc.
Basically, the Mamiya Universal is like an LF camera without movements (other models like the Super 23 had some back movements), so you have to work carefully and to check everything twice before tripping the shutter.
There are many resources on the web. Unfortunately, Bob Monagan's
Medium Format Photography Megasite is not fully working at the time, but you could check
Claudio Bottari's page.
Cheers,
Abbazz