Pulled from the CD-ROM:

WARRANTY
This engine has been produced using high technology materials and maximum precision machines. However, you have to consider that the severe conditions prevailing during competitions and the use of fuel containing increasing quantities of nitromethane constitute situations that cannot be controlled by the manufacturer.
We therefore regret that we cannot extend our normal warranty conditions to this engine.

Therefore, if you want to run a Fox plug, go right ahead. HOWEVER, if you want the engine to run well, I'd stick with the Ninja plugs. I'll just get a 5 pack (which is like 2 gallons of fuel) and call it a day.