IMHO it would be an advantage if the pad would be plugged into the control-frame from the bottom and not from the top and stick in firmly enough to not drop down by gravity+shaking.
Why?
Because I can imaging well sitting in a train, the train stops at a station, the doors open, someone runs by, pulls your pad out of the frame and is gone while you sit there for far too many seconds with an empty frame thinking "ermm...wtf!?"
Edit: However if the control-frame would be shaped like a boomerang you could strike the thief down like Crocodile Dundee and get back your pad while the crowd applauds.
