The cartridge type is known as a "captive piston". It uses a modest amount of smokeless powder, that drives the piston, imparting push to the bullet projectile. The powder gases have to be contained 100% inside the case, so the volume and pressure can't overwhelm the case to piston seal, otherwise it would be loud like any handgun.
Ballistically its very low power, very short range. None were intended as defensive because they just don't have even close to enough power or range. All were intended as silent assasination weapons. This particular Soviet design was meant to be used at contact distances, and the bullet is straight from an AK-47, so that afterward people would conclude the targeted victim was shot with an AK or SKS...not a tiny concealable handgun purpose built. So security would be looking in the wrong place at the wrong suspects.
Would it work? I'd guess yes. I'm sure the Soviets would have tried them on animals. And Afghan prisoners.
They also had a different design, a little like a Makarov, semi auto with at least 8 rounds. Before that, the OSS had a dart launcher using this principle that mounted to an issue 1911a1. And there were rumors of a CIA 12g cartridge launching a big dart silently.