It's a one handed keyboard. For people missing an arm, or with like... palsy and shit. Used to work with a bloke in Townsville that used one because he had a stroke or aids or something, that stopped his left arm working. Kept up with the slowest typists in the room (the 40wpp crowd)... so I guess it works ok.
The only problem was that every time he started a shift, a two hander would have to plug in his keyboard for him.