The server I saw it on I never actually got to use it (class based zombie hunting server [human vs. npc, health system, no tagging]). To get classes you had to do something specific multiple times. Neckbreaker went with CQC class, which required 6 knife kills. Saw one guy use it a few times though, it was pretty cool, mostly got in the way on that server though because you can't hide from npc's, so you just had to stun them (flash) everytime you wanted to use it. Would definitely be really fun to have here, don't know how we would unlock it here though.