I wish I had one of these to cancel the fireworks in my neighborhood that have been going off all week into the night

This is absolutely fascinating and the first I've ever heard of such tech. As a musician, I'm excited to see where this may go? Thanks for posting!

Landlords will still never put these in, I suspect they like the noise complaint calls

The problem with all of these devices is that there is a lot of noise power in the world. A jet engine is loud because the acoustic energy it produces displaces large volumes of air very quickly. To cancel that energy, you also have to move huge volumes of air. Headphones are good at this, in part, because they attenuate so much energy in the first place with an over ear headphone, or well sealing IEM, and place the speaker very close to your ear. A source of acoustic energy which is D meters from your ear has to produce at least D^3 more joules than a speaker right next to your ear, to cancel the same amount of noise. It's possible, kind of, with very big speakers, but a handheld device just won't cut it.

KDE devs are really branching out.

That would be cool. You could live right next to train tracks or an interstate and not have to hear it