Zombie Knives are distinct from some of your other knives. They need certain characteristics, and a proper zombie killer should plan ahead:
Zombies move erratically, and might have random leftover steel plates or pins in them. You might want a folding knife for the convenience of carry, but they risk getting closed on your hand and cutting your fingers off when that zombie makes a random lurching move while you stab it (this makes for little zombie fingers crawling around...). Therefore, you need something that shrinks like a folder, but cannot close on you when in use.
Balisong:
Lets say you're up against a Cyborg Zombie (yikes!). you'll need something that is capable of severing the titanium sheath that encases it's undead cybernetic spinal cord...you need tool steel for that:
Then there's the times when you need a quick response knife, for those times when you got your others stuck on particularly dessicated zombies who then ran away. This calls for an automatic:
Finally, you need something a bit classier for when the King of England wants to throw a ceremony for you after you defeat the zombie armies. Also, this classier knife is useful when that supermodel-turned-zombie comes along, and you want to go on a date before dispatching her...
PLANNING is the only thing that will get you safely through World War Z.