Here's my .02 cents worth. Keep in mind I'm a natural born cynic (and an aerospace engineer) so you've been warned.

To say that Evo's are just rebadged MVVS's is incorrect in my opinion. The gas Evolution engines are simply reverse engineered versions of MVVS engines. While they are obviously designed to the same configuration, a side by side bench top inspection would most likely yield large differences in casting quality, machine finish, and metallurgy. This obviously effects power output, longevity, and reliability.

The Evo's are probably made in China who are the experts at reverse engineering. Keep in mind they can't manage to make dog food that won't kill animals and your children just might be sucking on a lead toy right now. If it sounds like I'm frusturated about this, its because I am. Evo has stood on the backs of MVVS and copied their engines and is now selling it with reduced quality and larger profit margins. This undervalues MVVS engines and stereotypes them as junk engines as well. If it looks like an MVVS, sounds like an MVVS, it does not mean its an MVVS.

Also notice there are no more USA distributors for MVVS--this is basically a marketing blackout to push Evo gas engines on the sheeple that think they're the same engines. Its certainly not a coincidence.

Moving back to the original question, Zenoah engines are still well made engines that are as reliable as a stone axe. They only have two weaknesses. They are converted industrial engines and therefore are heavier than they have to be to get the job done. Also, the lack of ignition advance robs them of ultimate power. The latter can be fixed by using a CH ignition. Depending on your static balance situation and power required these issues may not even be a problem.