I have a few of them, Balda super baldesa, a few Ensign's and others, and providing the patch is fine then I have no problems using them, remember that most are 60+ years old and the patchs do fade, but get one in good condition then focusing is a doddle, for those folder's, and others that don't have a rangefinder I use a simple shoe mounted rangefinder, in my case a watameter, cost me under £10GBP, and again works a treat, I find Folding MF rangefinder's a lot easier to focus than 35mm folder's or even the 2 or 3 Barnack leicas that I use. and all the cameras are single window rangefinders, there were a lot made, and still a lot around, in fact, there were more single window than double window sold, at least over here, I take it you are looking for MF folders, if 35mm comes into it then look at Vogtlander and their Vitessa range, fine cameras and unusual with the barn doors,if fact too many to list here, but all easy to use and a lot of fun,