I used the powergrips for a while. I 'graduated' to clipless. I thought the powergrips were OK but not great. Accelerating from light was always a bit tens trying to put in the left foot by feel. I got good at it but the other thing that wasn't so great was the pulling back action at BDC - my feet would tend to disengage a little bit, requiring me to re-position often.

On the whole, a plus, but not as good as my eggbeaters.