I, personally, would find this useful for doing work with a photo editor, 3D modelling tool, or some other program where I would otherwise be rapidly switching between keyboard and mouse.

In terms of raw typing speed, I don't think that it can ever come close to the performance of someone using a machine-optimized keyboard layout with two hands, but I very much like the idea of not needing my right hand to dance back and forth between the mouse and the right side of my keyboard.