I use these too, great value plugs, but on a modified engine, look to change them frequently, I swap mine out every other race meet. But at less than £10 for a full set its worth it. Certainly they do as well as the £40 Irridums I used to use.
It's certainly worth it, I use these everytime I replace the sparkplugs. Some employees at stores refer me to other expensive spark plugs(probably for more revenue), but I recommend these. Exceptional with regular use, and looking other posts here, looks like it can do with racing use if need be. But for regular use, I don't see any reason why you shouldn't get this plugs.
