a088008,

I think you will gain a little in efficiency just by not having the gaps you would have with ailerons. On the other hand, increasing camber when you want to increase CL is actually better than increasing AOA, so you don't really gain by avoiding the camber change. You might also give back some efficiency at the junction where the tip panel pivots. Overall, my armchair assessment is that the overall drag will be similar to that of a conventional aileron system. I could easily be wrong about that.

Regarding flutter, I don't think it matters where the center of mass of the tip panel is; weighting the leading edge per se will not help you. You can 'tune' the system by changing the overall moment of inertia, but the weighting the leading edge is only one way to do that. It is true that pivoting near the 25% chord point will minimize the torque required. Rather than going back to 30%, I would recommend that you go forward to around 20%. You want the aerodynamic center of the panel to be behind the pivot, for stability.

Good luck, and post pictures,

banktoturn