I've been using my Aztek A470 for about 5 years now. I have also used a Paasche H, Badger 100G, and Badger 175. I think the Aztek is a great airbrush but has one flaw, you aren't supposed to break it down. I think Aztek really dropped the ball on this. I've broken down my Aztek a few times. After reassembly, the airbrush worked like new. The problem most people have is air leakage. What I have noticed is paint building up behind the washer. This stops the needle from seating completely resulting in air leakage. As soon as I clean this residue off, the air leakage stops.
I agree 100% about "it's the modeler, not the tool". I've done freehand camo (ie no masking) on 1/35th armor using a Paasche H. Many people would say it's not possible. Good looking paint jobs are a result of understanding paint, thinning ratios, distance, speed, air pressure, etc. Personally, I've never understood the need for some people to pay $400 for an airbrush to paint models. If I was a professional artist, maybe, but not for a hobby. To me, buying a $400 airbrush for a hobby is like buying a Lamborgini to drive a commute in city traffic.
-Jesse