OS all the way, best reliability.
did some experimenting with the last Rossi ducted fan engine, it was the follow up for the 90, I think this was the 102.
it would not idle without a glow assistance , but if just left on full power it was really strong, very unreliable though, and it used conical glow plugs for whatever reason, Real Italian breed for sure. Oh, and NOISY !
even the Rossi 90 was pretty finicky, but decent if you got used to it.