I know of several guys and gals that use those cheap knockoffs. Most of them are like the Master airbrush, etc,etc. I have had my share and some were pretty good and some were, well you get what you pay for type. At 21.00 if something goes wrong you and always go and buy another one but with a quality one then there are repair / replacement parts. I bought just recently a Paasche Talon that includes 3 sizes of spray tips and nozzles and it even includes a fan spray nozzle. I also own a Grex and a Sparmax which both work exceptionally well.
In the end do what ever makes you feel warm and fuzzy but I would just go with something of a higher quality that will have a warranty.