The Bookends one is pretty pricy IMO...
I read before the users just use a USB hub and connect their mouse, keyboard, printer to one usb port just to say a few seconds...
IMO, i don't really need it since its a PB.. you have the trackpad, keybaord and screen.
You can always go wireless(bluetooth) with the mouse and keyboard if you wanted since the PB has bluetooth built in.
Save your money and get a good secure lock to lock it up ..