The biggest problem with them, when you're on approach and move the ailerons, you dump the extra lift created on one side.

IF you're going to do it, make sure its on a plane with full span ailerons, doing it on anything with wing tip ailerons is a BAD thing, you're creating wash in, which is the last thing you want during a landing approach.

They can be cool to play with but definately not while you're learning to fly.