These have been around in some form or another for many years. I'd discussed them with one of the local wardens years ago,, and at least around here it would be considered a firearm as far as bow hunting goes. At least can't be used during "Bow Season" according to the powers that be. And iffy for bow fishing in some areas,, here it's legal to shoot fish, so not an issue here, other places,,,, who knows??
I've made some up in the past from brass tubing and found them to be less than useful for most things,, range is limited, power is limited and there good for one shot. In fact they can be down right dangerous,, I had one come zinging straight back at me before,,,,, NOT GOOD !!!!! It's not the "better mouse trap" they make it out to be. And in some areas it could be considered to be a destructive device,, by the letter of the law,,,,so be careful till there classified one way or the other.
There nothing more than a mini "bang stick",, just launched from a bow.