a friend of mine in an airbrush educator...
here's what she told me about what to pay attention to when you wanna buy one... (it was in French and my English is not perfect)
to sum it up: a compressor of at least 4 bar with a position to make it stop automatically.
an aero with a 0.2mm buse and pref evolution, focus, utlra, do not get an old one or do it know what you do telling yourself that you'll have to buy a new (round €80) saving on the compressor (but not that much)
she works with the STDS products