I'd not heard of hobby scale water curtain spray booths before either, but there appears to be at least one company making them,
Hseng.
From what I can tell it seems mildly gimmicky. It still has filters you need to change, so you're not saving any money in that regard, except maybe you're not changing them as often?
I also can't tell if you have to have it connected to a tap or not. If you have to have it "plumbed" then that's a major consideration to take into account. If your hobby space isn't close to your bathroom, laundry or kitchen then it might be more hassle then it's worth to find a way to connect it to a water source. And if it's got an internal reservoir, how long does that last? How often are you filling it up so it can keep providing a curtain?
Also I feel I need to ask, what are you using in your day to day painting that's giving off fumes? I don't see how a water curtain could make that much of a difference in that regard?
Personally, unless there was a very compelling reason to have one, I'd skip it and buy a regular spray booth.