Even though it may say that it's broken in at the factory, it's better to be safe than sorry. I will usually put 2-3 tanks of fuel through the engine (following the break-in procedure in the engine's manual) before I put it in the air. As Bubba said, a good break in is probably the biggest key to having a motor that will last a long time. OS engines are very reliable and will give you great life if you break them in properly. Just follow the manual. I've got an OS 46 FX that has over 500 flights on it and I've never had a lick of trouble with it. It starts on the first or second flip, and is still as strong as it was when I got it.

Ken