I think it is gimmicky. But looks like the idea is to create a larger wound very quickly. In theory that should stop a threat sooner.
I think so too. If this works as shown the cavitation would cause a good deal more damage, but he stuck a watermelon. It would be better off using ballistic gel, or even better a hog carcase.
Yes the first video explains it was for divers. They stab the fish, it shoots it full of air so it will float the body to the surface. Also the wound is somewhat frozen and will prevent some bleeding so as not to attract other larger predators to your location.
ohh interesting. I suppose that does make sense but it would be pretty tough to use properly i'd think. But i guess if you're spending $500 on a diving knife you are probably pretty good at both stabbing and diving.
Here's another odd one I've seen, three blades, looks like it'd be a bad day if someone stabbed you with it (not that I'd consider it a good day if I was stabbed with a regular blade).
http://www.ohgizmo.com/2012/04/05/jagdkommando-dagger-has-twisting-blade-for-100-more-killing/
Needs a way to auto-trigger when fully inserted and beginning to back out.
	