Someone that I fly with has the OS and loves it. I've got two of them. Eventually they will be going in a twin. Started the first one yesterday, and only one tank of fuel so far. If the ground testing is any indication of how it will do, it's a great engine. It's in a small Cub ARF I got off of ****. Hope to put it in the air today (guess I'll have to change my sig). If I do, I'll try to post a report.