I did some research before I bought a KopyKake airbrush because I had the same question and it seems like a lot of the craft ones are too high pressure for cakes, especially buttercream. That is what you should look out for I think. Otherwise it probably is okay as long as you only use it with edible coloring.
I believe it's ok... however, I don't really recommend it. I tried KopyKake during my training class and then I bought one from HobbyLobby ("Paasche" brand), I do really feel the difference. The one from KopyKake gives much more nicer & softer looks than the one I bought from HobbyLobby. Not sure with other brand though.
If you want a very fine detail, I heard Iawata is the brand to go. And there is also Badger for extreme detail.
Hope that helps.
It looks like the compressors for cake decorating are in the range of 0 - 30psi mostly. Seems like the compresser may be the most important part but I am pretty sure it is the priciest part of the kit as well. A really good Kopykake compressor is around $150. At the bottom of the Sugarcraft page for airbrushes there is some input on choosing the correct airbrush: http://www.sugarcraft.com/catalog/airbrush/airbrush.htm
Hope that helps!
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