Such a device would be perfectly feasible as a one or two shot proposition.
But nothing like that would be approved for import. It might not be illegal, but it would fail any "sporting criteria" test. BATFE has classed similar devices a AOWs, under their somewhat flexible reading of 26 USC 5845. Could you make one under your license? I think so, but if you sold them to the public, even as AOWs, I suspect BATFE would figure out some way to stop you. I notice one of the devices pictured is a mockup, and I notice that the devices seem to come from the UK and Japan, both of which effectively ban all handguns; I suspect there is not, and never was, any working gun, just a teaser to tick off "authority" and cause panic in the TSA.
Let us know if you are successful in finding a source.
Jim