I can add my own testamonial if you'd like:
I've tried quite a few brands of snake oil, and none of them have done dick-all.
I think the companies work on the idea that if everyone only buys it once, they still make money. Thats why there are so many different brands produced by the same company.
At the end of the day, if you feel that you are helping protect your engine with magical fairy dust then thats fine. I'll stick to the tried and tested methods of good maintainence instead of a lucky charm.