Most of the "broken-in" or "pre-run" engines that manufacturers offer are still not completely broken in engines out of the box. Usually these engines will come with a piece of paper inside the box that says you need to run X amount of cc's of fuel through the engine being easy on the throttle then you can put a race tune on it. If it were me, I would just buy a normal engine, send it to a reputable engine service, and have them break it in. Then all you have to do is throw it on the track and adjust the tune for your area. No additional break in needed. But I also prefer to break in my engines myself. I use the "Bess Method" and have never had any problems with my engines using this method.