Pretty much every engine manufacturer I have gone through technical training with (Honda, Kawasaki, Bombardier, Yamaha, Mercury as well as their marine platforms) have recommended NGK pugs. Basic foundation for their engineers recommendation.. as well as the companies heat range tunability to their engines.. is the titanium construction of the metal end of the spark plug (threads and exposed portion of the spark plug). NGK was one of the first to adapt it to their spark plugs. Aluminum engine heads, especially air cooled, see severe temperature changes. These changes in the long run act like blow torch welding of metals together. Issues with other spark plugs welding themselves into the head are not seen with NGK plugs. Since the days of aluminum automobile engines and fuel injection system advancements as well as raised exhaust temps, many of the spark plug manufacturers have followed suit as titanium coating of plastics, ceramics and metals has advanced and adapted in fuel/exhaust systems components in the high temp aspects of engines and performance. Quite a few of the spark plug manufacturers have stepped up to this technology as result of the fuel crunch of making low octane fuels burn in the combustion engines require more heat. They have tried to 'reinvent the wheel' by theoretically adapting more electrodes , tip coatings, other thickness of electrode wire and center fire plugs to keep up with the heat needed in low octane high heat fuel economy engines. I have been sold on NGK's since the get go because no anti-seize is needed on their spark plug threads since the beginning of time. Plain and simple, their construction of the basic spark plug well surpassed any and all manufacturer demands before even threaded into the head. I'm not trying to push NGKs on anyone but have torn apart spark plugs abilities and drilled manufacturer engineers with questions over the decades I have been in the field. I'm not an expert, heck, I still stand behind single electrode plugs as well as indexing them for more performance. Anything else hanging off the tip of a spark plug inside the combustion chamber is to me ether a heat sink or a potential problem in combustion direction or accelerated cause for further part failure in the long run (Uneven combustion, hot spots, cold spots). Not taking pot shots at anyone, just stating my old school proven theories that have stood the test of time... besides, I really don't care what you stick in your weed eater for a spark plug.. I know what I install in my engines !! LOL ( and I most likely can't be swayed from my thinking on this one)
~Gimpster~