I do confess I haven't read this whole thread.
But I've been flying my Mayhem since last winter, and I've flown the crap out of it.
My big complaint is that I've bronken two of the mylar CA hinges (one on the rudder, the other currently broken on the elevator).

I use a Super Tigre .90, but my buddy has the same plane, and he uses an O.S. four stroke, and it flies it better than my engine.

A great flying plane, I'll buy another when I crash this one. But I'll do the hinges differently next time.