Summary: I bought this because I was having shoulder/elbow pains from holding my arm out to move a mouse. I'd hoped that this keyboard would eliminate the need for that, and I think it would have worked had the execution been better.
Pros: A good concept, but doesn't work well for me in practice.
Cons: The trackball is too small, too stiff (takes force to rotate), and too slow. I had to rotate it several turns to move the pointer across my screen. Also, the keyboard keys are too stiff for my taste: a keypress takes more force than with most keyboards. This was particularly true of the space bar: my normal typing force caused about half my spaces to miss.