Is it difficult to apply either of these paint protection sealants? I was reading the instructions on an Ebay auction, sounds simple enough but have had problems in the past with some waxes leaving white residue etc.

Dead easy just take it a panel at a time.

Has anyone bought the stuff off eBay - is it OK - can you recommend a seller?

Its easy enough, just the same as regular polish. Just try to apply in straight lines not circles.

And you car has to be spotless before you put it on.

Has anyone bought the stuff off eBay - is it OK - can you recommend a seller?

Yep, I went with Diamondbrite for my current car (getting mt Furby VRS this weekend, the dealer threw in the Supaguard for free, woo hoo)

No hassle at all really, and makes washing it a doddle. Just make sure your paintwork is spotless first. Definitely worth a shot if your car's black, mine's a pain in the @rse to keep clean...

Thinking about it, I never did the alloys with it, but have some left over so might use it on the Furby when I get it...