I have a KopyKake. I can't speak for other brands because it's the only one I've ever used.
One thing I really like is the adjustable air pressure. (I assume all brands/models would have this, but just in case they don't...)
What I don't like is the tiny color reservoir on the airgun that comes with it. It's fine for doing little to medium bits, but you have to refill over and over if you have a big area to color. If I ever get around to it, I'll get a new airgun and/or reservoir.
I don't think they require any particular ink (food color). There are several different brands of airbrush food colors available, and mine doesn't seem to care what I put through it. I've even put luster dust mixed with clear vanilla extract through it without much issue. It clogged a couple of times, but I just blew out the clogs and carried on. I've just ordered "official" airbrush pearl color, so I'll see if it clogs any less.
HTH!
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