Given their simplicity, I would think that Mamiya Press cameras would also be very reliable. Their lenses are like large format lenses, which last forever, and it's easy enough to adjust their focusing mechanism.
I have a Mamiya Universal, four lenses, four backs, and various other doodads. Overall, I agree that the system is pretty reliable -- it's quite simple and built very sturdily. However, age and time demand their due.
I've had minor issues with one lens and moderate issues with another. My 6x7 back, which seemed lightly used when I bought it, crapped out entirely a dozen rolls in. There have been a few other relatively minor things. I'm not arguing that the system is fragile -- it certainly isn't -- but it's also definitely not immune to the wear and tear camera gear can accumulate over decades, despite being a family of pretty beastly metal contraptions.
I'd agree, not to mention you have even more format versatility with the Mamiya Press system -- 6x9 is included.
It
is amazingly versatile with regard to formats from 645 to 6x9. I even have a 6x8 setup for my Universal, using the G-adapter and the 6x8 back for the RB67. Easy. Works like a charm.
Versatile in lots of other ways, too, much more than we generally think of for rangefinder designs. I sometimes like to imagine the sort of generalist professional photographer who would have made full use of this system in, say, 1967, from shooting events with roll film, to architecture with sheet film, to portraits, to macro shots of small objects, to copying artwork, etc.