It seems like a good spark plug tutorial. But, just like a recent similar link to a synthetic oil article, to me it sends a message to use Autolite Iridium XP in all applications. Maybe they make more profit on those? I believe there might be some subliminal vibes being sent out to the tune of good, better, best. For just a few dollars more, why not use the best for "improved engine performance and emissions". It also seems to address that problem they bring up of people choosing not to follow any plug replacement schedule.
A pleasant read, but nothing new.