Hi Ruben,
OK, that was not particularly detailed, I admit, but I didn't want to get into a generic discussion of the Zorki's viewfinder system 🙂
Like some of the earlier screwmount Leicas, the Zorki has a dual viewfinder setup with two windows at the back, about 2 cm apart. The left one gives a circular view for the rangefinder, which is very, very squinty but has a magnification of 1:1. The right one is for composing and gives a rectangular view which roughly corresponds to a 50mm lens at a magnification which looks like 1:0.5, also quite squinty.
Because we have two windows, we can evaluate rangefinder operation and framing accuracy separately. The rangefinder feels reasonably precise, mainly because of the relatively large magnification. Framing for 50mm lenses, on the other hand, is a matter of taste, to put it diplomatically. Personally I think the Zorki (and the screwmount Leicas) viewfinder is a disaster, possibly the worst viewfinder I've ever looked through. The cameras have a cult following, so apparently it works for some people, but I am not one of them. I ended up using it only with lenses which require an external viewfinder anyway, largely the 21/f4 (where focusing is unnecessary) and the Jupiter-12 with a Helios finder. That is a very workable combination. When focusing this combination, I mostly leave my eye where it is and move the camera diagonally. The disadvantage is that the distance between the leftmost rangefinder window and the accessory shoe is quite large, so that I have to shift the camera quite a lot. As long as you and your subjects don't move, though, this is not much of a problem. Note that you have the same procedure with most other FSU cameras as well excepting possibly the Drug, because the viewfinder on all those gives a 50mm field of view - so here operation is exactly the same as on any other FSU camera, except that the whole thing is more compact.
Later Leicas have the windows closer together, which for 50mm lenses makes operation easier because you have to move the camera less.
A camera with a good 1:1 viewfinder, like the Drug (which I've tried) or a Bessa R3x (which I haven't), beats the Zorki's (and the original Leica's) viewfinder-rangefinder combination hands down both on rangefinder and framing accuracy. The advantage of the Bessa T in this respect is that its rangefinder magnification is even larger at 1.5, so you can focus even more precisely. Whether the whole system is more precise than even a Kiev (with its enormous physical baselength) seems somewhat doubtful to me, but it's probably less squinty. Incidentally, if you use a Kiev with an external viewfinder, you already get a pretty good idea of the operations involved, only that they're easier on a smaller camera like the Bessa T.
What I would have liked about the Bessa T is the externally-readable exposure meter. A very good idea. If I were to duplicate Huw Finney's TTL Leica III project, I would put in an external set of LEDs instead.
I suggest you get a Zorki-1 from somewhere and try it out. Even if you decide two-window operation is not for you, they are nice cameras overall, reasonably cheap and you get an impression of 1930s photography. (And by comparison with your Kievs, you get an impression how vastly superior the Contax was over the Leica!!) I got my Zorki-1 from a RFFer when preparing a seminar talk on Bateson and Mead's photoethnographic projects in Bali in the late 1930s. Being able to give students a Leica lookalike to play with was very useful in getting them to understand the parameters and limitations of photoethnographic work at the time.
Philipp