I have repaired enough Iskras to know better than to buy one. It is not only a matter of build quality and materials, but who has been tampering with / using it. Grease in the shutter blades (yes, grease, the yellow-brown stuff, and when cleaned it stopped working, just a coupled of bent pins, but the previous "repairman" left it almost useless), the shutter button linking bar replaced by a lollipop stick and lots of glue... Too much of a lottery for my taste. Bellows tend to be usable, though. I own several folders that I like best (and I think are better, but that's just my opinion, there is no "best folder ever"), and I happen to own several Ikontas. Despite I don't like Zeiss glass too much, the e.g. Super Ikonta 532 I own is far better (again, in my opinion and taste)
Actually, one of the main reasons you find Iskras with the red window, apart from dead advance mechanisms, is that owners wanted it that way: if you open the top cover and know what you're doing, it's easy to see that a wheel and/or a spring have been removed to avoid engaging the system. But, in most of these cases, there are two red windows, since it was used for 6x4.5 portraits.