I've seen them used on a couple of things. The chrome is very impressive, but it is a complex process. Candies are difficult to apply well, and require some good spraying skills.
Same thing here, but a couple of bucks cheaper:
http://www.kustomrides.com/supplies/...ray-paint.html
I've never found a spray can that shoots as well as my airbrush. The droplets from a can are usually just too large, and you end up with too much orange peel. I might give 'em a try though.
Which ones are you looking at?
Steve