The earlier Zorkis and Feds are true Leica LTM clones, including bottom loading and separate rangefinder/viewfinders (a disadvantage IMHO).
Later Zorkis tend to be (sometimes much) better made than Feds. IMHO later Feds are pretty rough, in a way which won't clean up with a CLA. Also, cameras from the 1950's and 60's *tend* to be better made than late 1970's and later cameras.
In any case, a *good* example, or by now a CLA'd one, can be a very nice and reliable camera.
Simply buying one from anyone is Russian roulette (pun intended), but a good one is a keeper.
Later Zorkis are actually Leica LTM improvements, having back loading, bright, combined RF/viewfinders and sometimes other features.
Favorites: Zorki 3 for looks and feel (though some slow speeds are sytematically inaccurate), Zorki 4 for all-round (later one have painted-on & not stamped & painted shutter speed dials), Zorki 4K for its lever advance (but also known to cause problems), Zorki 5 & 6 for wider rangefinder base, lever advance & hinged back (IIRC) (but missing speeds under 1/30).
The Jupiter series of lenses are derived from 1930's Zeiss lenses and are still very good today (given a decent sample). The Industars are Elmar-derived and also usually quite good.
BTW: The Kiev Hasselblad clones are normally extremely shoddy and unreliable unless they have been properly rebuilt. On the other hand the Kiev 60 can be quite good, with a few caveats thrown in.