I owned three Kwik Built's...2 Mustangs, and the Super Chipmunk. All of mine flew very well...maybe a little heavy for the wing area, but nothing serious. The only problem with the design was keeping the plastic shells stuck to the tape on the fuselage. I glued the shells together along the seams with a thin strip of ABS as a doubler and it helped a lot.

I tried to buy a Mustang kit recently, but the guy wanted way too much for it. I had one of my most spectacular crashes with a KB Mustang. Full power dive and pull out low over the runway. Just as the plane reached "crowd center" the left aileron fluttered and ripped off the wing. The plane cartwheeled in the air and was blasted into a million pieces when it hit the ground.