Anytime you can put something in the spectators hand and walk away for them to keep it, you create a
magic moment. Sometimes those moments are brief (as with leaving a signed card) and sometimes more
memorable (as with leaving a signed bent coin). "Card Cube" is memorable because you are giving them
something they have probably never seen before. You aren't just another magician restoring a signed
card, you have taken their card and created a very cool little prop for them. This is something the
spectator will probably keep on their desk or nightstand, and folks will quickly ask you for their
own.
You cannot do this with a signed card. Well, you can, but you'll have to create the
cube with them watching. For the effect as demonstrated, you'll need to do it unsigned. Also, the
effect itself is a little weak for such an impossible ending. You'll want to create your own routine
to make this something amazing.
Creating the cubes takes a few minutes, but once you get
the hang of it you can run them out rather quickly. Spend one evening watching TV and making cubes,
and you are set for a long time. This is an effect that will set you apart from most of the crowd
not because of its difficulty (it's a beginner trick at best), but because of what you leave in the
spectator's hand at the end.