I have a Rolleicord III, 75mm f3.5 which I inheireted from an uncle of my wife's ove ten years ago. It required a servicing, which included aligning the the top lens with the bottom (taking) lens. I have since shot many rolls of film through it. The lens quality is very good, and yes, I agree that the corner and edge sharpness suffers at wide apertures, although the centre part is very good wide open.
This is the only Rollei that I have owned, so I can't compare the results with any others, but I have handled the Flex's, and I agree that the egronomics are a bit nicer.
I have a 50in. wide high resolution print (on a Durst Lambda) from a scanned (drum scan) transparency, and the result was spectacular!
I intend to keep shooting with this camera for many more years!
Keith