[citation][nom]sliem[/nom]Broken hinge on this = broken mouse[/citation]
Nah, you're over-thinking it. The key-cover will be just that, a cover. This thing should be able to work as mouse and keypad simultaneously. In fact, if they were smart, they would put left and right-click buttons on the keypad too. That way, when entering a bunch of numbers into a bunch of different fields, you could keep your fingers on the keypad, move the mouse around, and select fields without having to open and close the thing.
that's how I would have designed it anyway, if I had come up with the idea.