Yeah, they do! And would solve a huge problem if they are legitimately functional.
So far, the US Department of Agriculture doesn't require a permit/license for a pet fish.
The US Fish and Wildlife Service doesn't require a permit and import license for pet fish, and so they do not have to go through the "special entry port" that a fish being bought or sold would have to do.
The US Customs has no problem with them, as they are very low-value.
The state in in the USA we're going to is still to respond as to any restrictions, but I'm not expecting any.
The US TSA (the security at airports) has no problems with them. Checking the UK version of same....
Hypothetically, if the bags work, the fish could go in my carry-on-fits-under-the-seat-in-front-of-me luggage (as pretty much the only thing in it) just fine. The airline wouldn't need to know.

But yes, I'd probably still make above-board arrangements with the airline and put them in like a box in a small dog kennel or something for the pet-cargo hold.
