I remember these!
Weren't they included with a dvd set or something? I personally think the tricorder remote included with the TNG dvds was a bit cooler but still a neat little gizmo.
All of those Japan ST DVD set premiums are cool...that they actually DO something is the remarkable thing. The TOS tricorder AM/FM radio-EMF detector is my personal favorite. This is the first time I'd encountered this PADD...thought I'd share.
At one time, they're running about on eBay. But I am not sure if they're the correct size to the actual prop, which I was quite sure to be 4 inch by 6 inches.