http://photo.net/medium-format-photography-forum/00TFHBhere it says that m645 comes with microprism focus screen, thats basically as good as as split image. that set is pretty nice since it comes with metering view finder, but if you do get waist level view finder, you need to use external light meter ince the meter on that set is built on the eye level finder. if your looking for square negatives, that camera doesent make the negatives square, but you get few exposures on one film than you would get with 6x6 camera like hasselblad. one more thing you should remember is that the mamiya doesent have film backs that you could change, so you need to use full roll before you can shoot other iso. but film backs cost bit, so if your not going to get more backs, its no big deal.
i dont agree with that must have digital back since those cheap ones that you might someday be able to afford have so small sensor that its not much bigger than 35mm dslr.
also film is not dead, its not long since kodak announced that new ektar 100 iso color film and i think it was this year when they announced it for large format also.
that 175$ for the camera sound suspiciously cheap, but maybe they sell for that price where you live. here they go for more like 400€ if in working condition, maybe 500€ since there is another lens and metering finder for it.