I use a Foca PF3. I like it very much - mine has the 5cm f2.8 lens, which is very good. I imagine that the 3.5 lens would probably be a Tessar copy, though I am just speculating, and I'd guess it would be a good performer.
The bugbear for me is the ergonomics. The distance scale is beneath the lens to one side - not a great location. The viewfinder is appalling. It's fine to focus through, but if you wear glasses, forget about it and mount an external viewfinder to use for composing after you have focused, which seems to be what Willy Ronis did with his. (As an aside, Ronis used the 50mm f1.9 lens, which is apparently excellent). And the final thing about the ergonomics is the winder: the film is advanced by turning the shutter speed dial. Less handy to wind on quickly than the film advance on a Leica screw mount.
Because of all this, my Foca is not the first camera I pick up when I want to use film. You compare it to a Leica. Having owned several film and digital Leica bodies, including ltm and M film bodies, I have to say that I even find the ergonomics of a screw mount body preferable. For example, you mention the combined vf/rf of the Foca. Well, that's fine, but don't forget that depending on which Leica screw mount you might buy, you will also have the lever to change magnification, thus increasing your focus accuracy. Also remember that the viewfinder and rangefinder on a Leica screwmount are handily located to the rear left of the body, whereas on the Foca they are central. And then take into account that the Foca vf is truly terrible. Leica cameras are, I would say, ergonomically superior.
But despite all of this (perhaps, in part because it adds some quirky charm and individuality), I absolutely adore my Foca and wouldn't ever sell it. If you can get used to its quirky ways the Foca is a great camera. If you're thinking of buying one then I'd check that the lens is clean, check that the shutter curtain looks okay, and check that the shutter is operating as it should. And after that, I'd buy, buy, buy and enjoy the camera if you're sure it is what you want. I love mine - it's my favourite out of my film cameras. But despite it being my absolute favourite, it isn't the first camera I reach for when I want to shoot film.
