I love the OS la engine but it is what it is, a bushing type airbleed carb engine. No comparison to the Evo engine's bearing and carb design. I have an Evo trainer engine that I took the flywheel off (lightened it up considerably) and now fly it on my Hanger 9 Twist. I don't think the Twist would fly nearly as well with the OS. Buy the Evo system and you will have no regrets.