I'd go for the Irvine .46 it will power you're trainer fine with a little throttle management, and you will still be enjoying it several models later.
I do not have any problems with all the other sugestions people are making, I have a Thunder tiger .46 that I picked up on Ebay very cheap and its a stonking little engine and love it , but boubt its any better than the Irvine.
The Jen is a Chinese engine rebadged for just engines, I'm sure they would not sell junk and its probably a good engine,,,,,,but the the Irvine is definately a good engine!.
OS make great engines I have a couple of their four strokes that are a plesure to own, but the la is very basic.
hope this helps
john