As as forum member HoosierQ once posted:
"To use a knife as a self defense tool against a determined attacker you need a tremendous amount of training...and then practice. Yes, the same is true for firearms but given the nature of the two different tools, the nature of training is very different too. In other words, there's a reason why people gave up edged weapons as quickly as they could manage to do so in favor of firearms. In a knife fight, say all the experts, you will be injured badly even if you "win"...you'll be cut up badly even if you make your attacker retreat. Such wounds may be life threatening. With a knife, you have no capability to stand off from the attacker...to be close enough to deploy a knife, he will be close enough to cut you. And of course if he has a gun...or a club/crowbar etc, he has totally got the advantage over you. It's just not like West Side story or Crocodile Dundee."
In other words, a neck knife has no reach, to use it as a weapon the potential attacker will have to be in very close, increasing their chances of getting control of your weapon(and potentially using it against you), and if they have a weapon even as big as a hammer, they can injure you without you being close enough to injure them at all.
