The Stowaway Keyboard is marketed by Targus, and is made by Think Outside.
It is 3.6 inches by 5.1 inches by .8 inches, only a little bigger than the Visor. Because of its small size, the Stowaway is easy to keep in a large pocket at school, or a small backpack pocket. It's very useful in that respect.
The keys are full size, and it includes a full ASCII set of characters thanks to a Fn key and a Cmd key. It also includes the 4 hardware buttons as keys.
One nice feature of the Stowaway is the stylus holders at the top corners. When you examine it closely, it is a very intricate piece of work. Flexible cables, no defects in the metal, it's high quality. When you are using it at school, you'll almost always be using it on top of a desk.
It works fine there, but don't worry about trying to use it on your lap, it works fine there too. Depending how I'm sitting, though, sometimes I put a book under the Stowaway when I'm using it on my lap.