I received one of these as a gift once. Played around with it for 2 minutes, then never used it again.

The main issue I had with it was that you had to 'hunt and peck' in order for it to register. Merely sliding your fingers around like on a standard keyboard would just register errant keystrokes.

Also, resting your palms had the same keyboard-mashing effect. It was cool to show off to others, but totally impractical for real use.