I agree with Ken and Jim. A plug will last for years if you treat it right. How do you treat it right? By treating your engine right. Fly with the engine peaked out and expect to change plugs regularly but fly nicely rich and easy on the engine and the plug will last seemingly forever. One thing that's hard on plugs is leaving the ignitor on while running at full throttle because then you have both the normal catalytic action heating the plug plus the electrical power. Like Jim, with CL stunt and always running rich I simply never even think about having to change plugs.