You can airbrush them on over everything... bare plastic, acrylic, enamel.
The buffing metalizers rub off too easy, but you can use the Testors clear lacquers (in the jars, not spray cans) instead of Metalizer Sealer. I don't like the sealer.
The best I've seen from these paints is to use non-buffing metalizers with no sealer or anything over it. The non-buffing ones don't have that rub-off problem.