has anyone tried this stuff? any good?

I havent used it - but if its to blacken your tyres, Meguiars tyre gel is brilliant, lasts for ages (and smells very nice)

I use Tyre Slyk (I think that is the correct mis-spelling) as recommended by Mark Underwood. Looks good when it first goes on and smells really strongly (but not unpleasantly). When the current can runs out I may try something else.