Good response to the questions asked Vic ..
No problems with being sceptical, I'm one of the biggest sceptics around and a debate can only be a good thing.
I can only go by what this bloke said when he used it. I haven't used it but am thinking of giving it a try on a couple of small scratches.
At this price, I think it's worth a go before a more expensive option (respray etc.) After all, if the scratch is that bad, what is there to lose?
Regarding the deep scratches down to the primer, after looking at the article again, the bloke says that a touch up pen is used in addition to the kit (sorry for any confusion/misinformation). As some said, that sort of repair not possible without the base colour.