It is my first DF engine - I bought it on ebay NIB with a new Byron fan and pipe for $201 US. I thought that was a great price, and from what I heard from others, the engine can be finicky to set up. I did not find that to be the case. Maybe I got a good one, or maybe I just have enough engine experience to set it up? Who knows but it is running much better than my expectations.

I also bought it with the knowledge that parts are not available (unless from private sources) as the engine is no longer in production. I figured even if I get one good summer's flying out of it I would be happy with the price I paid.

I have only seen OS 91's fly other than mine, I guess they set the standard in DF engines - but they are a lot more $$ even on the used market.

Probably best to ask someone with more experience with fan engines. Lots of them here, dont know why no one else is answering your questions...

Andrew