Eye tracking is useful if you can or want to sit in front of a desk. I'm concerned at the lack of diversity in eye-tracking manufacturers. Tobii is the only commercial brand I'm aware of or that Talon supports and initial setup requires Windows (I don't know if recalibration also requires Windows).

I haven't used eye tracking but I'd imagine that commands could be given in the short time that an on-screen element is focused... and the rest of the time the cursor jumps erratically.