Well I have one OS .91 FS and five Magnum .91 four strokes, and wouldn't bother with another OS. The Magnums start better, and I believe are better in every way with no less power, and possibly a bit more. I'm guessing that the carburettor has been changed from the OS design, hence making starting easier, and possibly the reason for a touch more power.

Magnums are last year's OS engines, but I think that the Chinese company (SY Engineering??) makes a few mods as well.

Magnum is the engine for me, and a bonus is that they are way cheaper than OS.