Is this stuff any good? My mate has had one of his locks popped out on his car and there is a bit of a hole where they put the screwdriver in, would this stuff be good for filling the hole then filing down.

ebay link

you might get away with it if the steel has been pushed in where the screwdriver has gone through. If trying to fill a big hole you might have to put a blob in from the back. As with any holes in this steel the problem is preventing it falling out when sanded down (eg if trying to fill in the punched hole where the lock is).

fibreglass from the back and std car body filler will also work ok.

I've used it for things like that and it works well.
BUT it may be cheaper to try your local motor factors for it first, I can
buy it locally for about 7 quid.