There is a review of one in the pRoducts review section of this site I wrote. I think the general view is that while they are a great idea they dont work as well as one would expect.
What i have noticed is that the box may say the PH is rated for X GPH
yet when I compair the intensity of the output of the powersweep with another PH of simular GPH
rating the powersweep always appears to be outputing a lower intensity. I think this is because they use an impeller that converts the water current into a side to side motion of the sweep head and this conversion must take a fair amount of energy out of the water.
In my view they also take up a significant amount of space.