I've had a couple different styles of these attachments, both the bar style and the round style. The bar style simply flops around to much, leaving one to spend all their time fighting the attachment. The round style does seem to work best. The heavier the weight, the better.
They do speed up the task probably by 1/2, perhaps more. Like has been said, they don't get right up to the edges and corners, but a follow-up with a fan tip can be done quickly and without spending too much time.
There is a caution with using power washers, whether fan spray or round sprayers, and that is that the will eventually scrub off the glaze of your concrete surface, especially if you run the pressure too high. In fact, with extreme pressure, you can easily gouge groves in concrete. Not a good thing. After you loose the glaze you'll end up with a sandy or gritty film that will have to be swept away pretty often. In some applications, that's fine, but just be aware that too much water pressure is simply 'too much'. I'm running about 2200 psi on my power washer, although it does have the 2750 psi max capability.
The pricing seems to be all over the place. I paid over $100 for the bar style, and ended up giving it away. Too much work to be useful. I've ended up with the round style that I paid about $70 OTD, and do like it.
They're definitely a good time saver, but not a total answer to cleaning surfaces. For extreme cleaning, I think you will need a hot water washer for the initial clean-up.
