Gus,
The main reason I want flaperons is for more lift for slower flight and landing/takeoffs. The Avistar has a semi-symetrical airfoil, and I've read it has about a 35mph touchdown speed...
http://www.masportaviator.com/ah.asp?ID=48&Index=6
I believe that the flat-bottomed airfoil trainers have a much slower touch down speed. I just figured it would be nice to get flaps on the Avistar to get the slow speed performance of the flat-bottomed trainers, especially for take-off and landing. The main drawback I've heard about the Avistar for a beginner is the faster speeds required for take-off and landing... and flaperons would seem to help here...