On my fold-n-fly the arms are semi flexible. They dont flex enough to vibrate but they do seem to stabilize the heli a bit since they angle inward just a a hair. Since I am using the Hoversport, which has no autolevel, any stability seems to be based a lot on balance and inherent mechanical stability. I bet if I put the battery up top it would not be able to handle it well. At the same time, my friend tried adding a little angle to his large hex using the WKM and he said it flew like crap. He went back to flat and it was much more stable. I think these controllers are more than able to accomodate the lack of dihedral. On a bigger heli, I would think rigidity would be more of an issue than the angle.