When you purchase this key, you get to choose which of the 7 items you want. This is not luck based

In the server you can choose one of these:

64 Cow Spawner

64 Spider Spawner

64 Zombie Pigman Spawner

64 Skeleton Spawner 

64 Creeper Spawner

64 Blaze Spawner 

64 Iron Golem Spawner