I have/had Ultimates, a Tecate, an ACE 4-60 and BUSA Phaeton 90 as well as other bipes needing completion. Yes it will roll slower than with 4 ailerons, but not so slow you would hate it. The top wing ailerons are probably larger than what they would be if it had 4 ailerons. My 4-60 and Phaeton (lower wing ailerons only) have adequate roll rates for the type of aircraft the are.