I got one of these after I killed a Cardian and really didn't know what to do with it. I couldn't sell it so I ended up throwing it away. A friend of mine got another one on a drop and tried to use it to control another of the same type but it didn't work.
Considering that each one is "specific to one card registration number", my guess is that the item can only be used to control the specific Cardian that holds it. As we get them on drops, this is useless as we just killed the Cardian that the card controls.
I was wondering, though, if a thief stole a Cardian's card, could he or she use it to control that card? Could someone try this?