Casey,
I've used MM metalizers for years - with excellent results. And I've definately achieved the best results using an airbrush.
I've used a hand brush many times, but only on smaller items - it really doesn't hand brush all that well because it's so thin and it dries so quickly.
The stuff can be quite delicate and most of the colors don't really stand up to handling all that well - they're ok once you use the Metalizer sealer, but that tends to dull off the paint a little, especially the buffing Metalizers.