The Norvel puts out a lot more power, but can be a bit hard to get running right for some people. Also, the Norvel has the most brain-dead muffler mount I've ever seen. You also should get the Norvel head wrench to be able to tighten down the head button, it sometimes comes loose, espeically during break-in.

The OS FP puts out less power, but is reliable right out of the box and will cause you no trouble.