My Mamiya 6 doesn't have a "preview", but it is one of the nicest-handling film cameras I've used. Very sharp lenses. The main problem is that after many years of SLRs, I often find myself with a blank image or two at the start of a roll (until I remember to take the lens cap off. )
I haven't been able to part with it even though I have done almost no film shooting for the past two-and-a-half years.
Eric