I bought the one linked to at Amazon, and it is on sale right now.
It paid for itself the first time I used it. I do my drive, and the walk ways around the house. The gutters drain onto both and turn them black, this device makes cleaning that almost instantaneous. I also found it works well of our fence (CYV) in the back which started getting black mold.
It is so easy and fast, I usually clean the black areas around my neighbors gutter when they aren't looking.
Amazon.com