I bought an airbrush a while back, along with an oil less air compressor. The brush is dual action, and was a bit intimidating. Last night I decided to put the thing together and see how it worked. I started by priming a miniature with boltgun metal, basically as a way to test how even the coats were, and to see if this gun would help me paint my grey knights. When I got home tonight I decided to try the gun on an Imperial Guard Punisher. I'm told the weapon is useless, but I like the way it looks, so I chose it plus three bolters as my first set of weapons to paint. After building the tank I primed it white, and then began giving the airbrush a spin. Most of this model was painted in under an hour! I has taken me two more hours to paint enough other parts (bolters, main gun, and tank tracks) so that I can use this guy tomorrow if I break my gaming fast. I am so impressed with this air brush I don't know what to say. You should just go buy one. I will never paint a tank by hand again. I even liked painting smaller objects like troopers and the bolters with it because it produces such an even coat. When I have finished weathering this tank I will post some more photos. The GW airbrush is already in the trash.
*EDIT A word of caution about purity seal. I used it on one of my heavily weathers tanks (not pictured here) and it basically removed all of the soot/rust/ash on the vehicle as well as changing the color of the graphite I used for worn edges.