The Kiev 6C,60 and some of the 88s take the same lenses. That means you can change bodies later if for some reason you don't like the body but like the lenses. Plus the same lenses can be used on a Pentax 645,Mamiya 645 and maybe others with just an adaptor.
The 1/30 sync speed has been mentioned but my Pentax is only 1/60. Not exactly a big difference. Unless you want a leaf shutter camera most will have low sync speeds.
OTOH other MF cameras are fairly cheap right now. Prices are a lot closer then they used to be.