That's a 'zip' gun. They have had them for years. Concealed in pens and all sorts of shit. Im sure you've seen them in the movies. most of which are home made.
Personally, you'd be an idiot to carry that thing. Esp in the USA or mexico. If you got caught with it you'd end in jail so fast your head would spin. Carry a real gun if you are going to take a risk like that. or dont at all or get a real permit
Just my two cents..