If you have barn door ailerons (scale in size and placement), then flaperons may not be worth doing, and it may make the plane prone to tip-stalls. If you have strip ailerons (non-scale), then flaperons might or might not be worth it, you'll have to try and see.

I agree with the rest of what causeitflies said. I've heard flaperons called "crash now devices". So, do be sure to try them up high.