GSI Creos is a legit company. Can't speak for their airbrushes*, but they are a big name with a reputation for quality when it comes to paints and tools for plastic modeling. Doing fly-by-night knock offs would be out of character for them.
There's a few of the major Japanese hobby companies that are getting into producing their own airbrush lines. I don't thing the GSI Creos ones are Chinese knock-offs, but they are very clearly derivative of Iwata brushes. Can't say how they compare to Iwata brushes in terms of quality, but I kinda think it's at least unlikely they're simply cheap knock offs. I would tentatively speculate they maybe have a connection to Iwata similar to Iwata's connection to Olympus.
Biggest issue is all of these (Tamiya, Wave, GSI, etc.) are currently intended for the internal Japanese market only, and so have no parts/service availability outside Japan. Though apparently some of the GSI ones have some part compatibility with Iwatas (and Airtex looks like it's just straight-up H&S-made brushed rebranded for the Japanese market).
In my experience Japanese hobby culture takes IP and product quality much more seriously than western hobby culture. Pirating and knock offs happen there too, of course ("Airtex"
looks like it could be a regional H&S rebranding, but the prices say otherwise), but they don't have the sort of casual acceptance they do here. I buy most of my my hobby tools from Japan these days, because they're the only ones in the world that still have abstract quality standards, while companies elsewhere have been tripping over each other to adopt the Harbor Freight model. I'd expect, say, Hobby Lobby or Games Workshop to start selling house branded Chinese ABs without batting an eye (they already do this sort of thing with their other tools), but not so much Tamiya or GSI.
*I do have one of
their airbrush filters, and it's good (I use it on a Badger air eraser), but a filter is simpler than an airbrush, so that's no indicator.
Mind you I'm not saying I recommend taking the risk. It's still too much unknown for the money when there are others that are known quality. Just saying I'm more inclined, on a purely academic level, to give it the benefit of the doubt.
