Well I have a Gaoersi 6x17 and haven't had a problem with film flatness, the 6x12 is essentially the same. They are no frills, but well built, and rugged.
I bought mine so I could use it hand-held if necessary, many places I shoot don't permit tripods. The 6x17's are adjustable to shoot 6x12, 6x15 and 6x17, they don't cost much more than the 6x12's. Personally I'm glad I went for the wider format, once you start shooting with it you're hooked.