ORIGINAL: cltom
I also agree about the flaps - they are almost more trouble than they're worth in a 15 size, and will make very little difference in the whole scheme of things at these sizes.
Whilst I can't disagree with cltom about sticking with stock unless you're comfortable with construction, speaking from practical experience with several Akromasters, the addition of flaps makes a notable performance difference with this model's aerobatic performance, and they are exceptionally easy to implement.
All you need is a piece of wire, an extra nylon control horn and a bit of fibreglass reinforcing tape and some tape for hinges.