> What's the catch?

Wide scale harvesting of water from the air will change the local climate in unpredictable ways?

One catch might be that it hasn't been tested at scale. The results are extrapolations from lab testing in a controlled environment.

There's quite a number of inventions and breakthroughs that looked great in the lab but never made it to real world applications.

Remains to be seen if this approach can work in practice and at scale and what the real-world implications would be.