A flat edge wing tip won't help the knife edge, but a flat plate will. The tip plates will help increase efficiency of the wing, and will help in knife edge to the extent that they increase side area. As for 3D flying and wing tips, it's pretty simple. Wing loading on these models is so low that anything fancy on the wing tip adds absolutely nothing to performance. The only benefit to a contoured or even a t/2 wing tip shape is purely aesthetic, which for some, may be reason enough to spend the time. I was actually considering adding some shaped blocks to the funtana 90 to make it look more like a scale airplane. The resulting performance differences would be marginal, and would go both ways. I would get a slightly better glide, due to the increased span, (2.5" ), but the roll rate may suffer for the same reason.

That's all I got to say about that.