Keep in mind that this is not a spray booth and does not pretend to replace one, so it is not fair to compare it to a different (and more expensive) product.
I have to paint on the computer desk so I have to cover the screen while airbrushing, plus do not have either much room to store a full size spray booth. As I only airbrush acrylics, I am not too much concerned about fumes. Nor I think the paint will bounce against the walls and come back over my model... At least with a home made cover, it has not happened.
Obviously, should I had a dedicated room my equipment would be different.
So, I think there is a market for different products.
P.S. I wish I could build things like that, and I know there is people absolutely able, but not my case