It's a novelty. Something more tuned for a scene in a movie than providing security for an individual.

But, the way I see it, you have the traditionally "solved" state cube on your desk(all faces complete), and when you want to use it as a key you "solve" the cube to the state that represents your key.

With a rubiks cube this means you only need to remember the steps of the algorithm that leads you to your key state.