actually i've read a lot that it's pretty useless.
you should definitely go for the "universal" version.
It is like anything else, it has its use, but if you don't ever need it for what it was designed for, it is indeed useless. It can help you keep things in focus. That is probably not something most people will use if for, but when needed, it is there. It will also help with magnification. If you don't ever want to use the back for that, keep it tightly closed. If you do have a need for either of those, enjoy what not many cameras have.
They are a little heavy, but with a wide strap, manageable. They are a system camera. You can change backs, lenses, and add extension tubes. The large negatives are nice to work with. The 65mm and 50mm lenses need separate viewfinders. They are both nice. The 50mm is a little large, but gives a really nice wide view.
The backs include a multi-format back. That is something I consider a bit useless. Why drop to a 6x6, and if you want 6x9, they have those backs too. Other backs include about three or four focusing backs. All but one take cut film holders, which can still me found from time to time. Beware the film pack backs which are sometimes advertised on the 'bay. Nobody I am aware of sells film packs any more.
The viewfinder has frames for 100mm, 150mm, and 250mm. The 250mm lens comes in two flavors; an f/8 and an f/5. The f/8 doesn't couple to the rangefinder, but is not as large. The f/5 does couple, but requires two men and a boy to handle. Alll Mamiya lenses are superb.
I keep most of mine in an aluminum case for transport, but not for carrying items. Already too heavy without the added weight of the case. A small (or larger) backpack with lenses rubber band wrapped in foam is a better bet. And unlike a 35mm system where you carry everything just in case, you won't do that with a press camera if you have many lenses and/or backs and accessories. At least I won't. In fact, there are times when I carry a Zeiss 6x9 for the big negatives and do without interchangeable lenses and backs.
Anyway, enjoy. Versatility in a 6x7 or 6x9 negative can get addictive.