OS is good but pricy, most are heavy for their power. Very dependable. If it was a girl you'd describe her as: "the kind you'd take home to Mother".

I have a TT Pro-46 that has sucked more dirt than Paris Holton - had the cylinder and piston replaced under warranty even though I admitted it was my fault. On it's third airframe having outlasted the first two. Now it sports a Perry carb as the original worked loose at the needle housing and leaked air (bent in crash). Shows no sign of stopping. "Racy".

I have a ST G-51 ringed and it is a snotty little engine. Noticably torquier than the TT 46 in mid-range but not much better wide open. Could be how I have it propped, though. "Tomboy".

Worst disappointment was the Kangke/SK-50 engine ($77 new; had to try). Broke it in with three tankfulls and then 25 consecutive dead sticks over two days with three good R/C mechanics scratching their heads and trying every trick known to rocket science. "Skank".

Evolution? Know of one being used. Works. No opinion. "Plain"