My philosophy is to build it with flaps, regardless of whether the plane really needs it or not. It typically only costs a couple of servos and a little extra time. If I don't use the flaps right away, I can always mix them out. Or, mix them in such that the flaps and ailerons act in combination as strip ailerons. Either way, you can first fly the plane like the flaps weren't there.

However, if you only have a 5ch TX with limited mixing capability, I don't think it'll be worth the exercize to get only ON-OFF flaps. May be this will be an incentivet to upgrade TX? Quad flaps are a barrel of fun.