I ran coro tip planes / winglets (not sure which they were technically-speaking) for a couple years on my B class combat planes. I found they had a couple of effects:

- delayed the onset of tip stall, so I could turn tighter. Noticeably tighter.

- decreased (eliminated) aileron flutter problems

- increased over all aileron effectiveness.

- (RC Combat specific) sometimes helped keep streamers from sliding off the wing. (note, due to combat rules, mine didn't extend forward of the LE)

If I recall, they extended up 2" above the wing at the TE and 1" below the wing. At just past the LE, they were about 1/2" above and below the wing