The EVO 10GX is messy for the first 2/3-3/4 gallon. After break-in it has deposits more than a larger gasser at 40:1 but way less than a typical glow. I switched over to synthetic after about 2 gallons and the deposits are less,
The engine is not that difficult to figure out. Pretty much it's ready to go out of the box as far as carb settings. Getting through the break-in is a bit messy but that's about the only drawback....if you can call it that.
It would be more than enough power for the trainer and he could stay in the air for 30 some minutes on 8 ounces flying a little over half throttle with power to spare.