A coupled rangefinder is a nice thing, but it's not that hard to get used to a shoe mount rangefinder, if you use it regularly. The Perkeo II does have a reliable frame counter that will always get you 13 exposures on a roll, if you want--not too useful for negative film, because the extra frame won't fit on a contact sheet, but it's handy for slide film.
I suppose we all have different uses for folders. I like them as handheld cameras, usually with fast film so I can shoot at 1/200 sec. or faster outdoors, and ideally around f:8-16. If I need a tripod, I might as well use a bigger camera.
Film flatness issues are the kind of thing most people don't notice without comparing results with a camera or back that has really good flatness, like a Linhof Super-Rollex back, which weighs more (just the back) than most 6x9 folders (the entire camera). Even the best folders are ultimately designed as tourist cameras, and this is where it shows up, in my opinion. That said, they are a lot of fun, can go anywhere, and can still give great results compared to 35mm.