Purely personal opinion coming up here
Of the ones I've looked through, both good and ratty ones, the viewfinder itself is not too bad, there are a lot worse around. What I found less easy to use (recalling handling one last weekend) is the RF patch is circular. If the camera is in good working condition, the focusing wheel is quite easy to use. Remember too that with these cameras you get 11 shots per roll, not the usual 12.
I prefer the 531/16 and similar, i.e. the one without the rotating prism on the lens. This is more compact, has a nicer viewfinder and the rangefinder is more distinct. There is also the uncoupled RF Mess Ikonta. I have the 6x9 version (524/2) with a novar and it is a very good performer.
The best viewfinder I have seen on a coupled RF classic folding camera is the Iskra. I'd guess that the Super Isolette, upon which it is based, is similar. If I had to select just one to keep, it would be the Iskra.
Anyway, you can always get a good one and try it out, as you'll get back pretty much what you paid for it.
Dusty, we await your images