I've been using an engine like this for about half a year now. No problems so far although it's really tight during break-in. It's fairly easy to adjust even for a (nitro)beginner like me!
This engine's pull-start is its only flaw. It's weak and won't last long so I would recommend a starter-box or something like that for trouble-free usage.
It could've had a bit more punch but for its price it's okay.
To sum it all up: It's a adept engine that's easy to use and start after its break-in, but its pull-starter is a bit on the weak side though it's great in the beginning!