Looks like you can have your own little dyno plus a whole lot more. When you go to the link below, don't forget to click on the video link ( below Nightrider Parts ) to see what it does.
I don't think so. The only real tuning usage would be if it could log A/F ratios with a wideband O2. I would compare it to measuring the speed of a fast ball. You can buy one of those novelty baseballs that has a timer in it to measure your fast ball or you could use a radar gun. Radar gun (the dyno) gives actual speed. The timer ball gives a less precise time vs distance equals speed, which in the case of hp would be speed /a constant cubed multiplied by weight equals hp or something like that. You could get the same results with a stopwatch and calculator.