It does a good job only if the vehicle is moderately dirty, otherwise you need to rewash it a second time. It seems to leave noticebaly less swirls.. also I apply no pressure at all and do soak the vehicle with foam gun before and during the washing.
I've never been a big fan but I do use smaller brushes to wash emblems, along shut lines, etc. Like LINKMAN said, they're OK for light washing when the car isn't too dirty. But it doesn't have the frictional cleaning ability of a mitt or sponge. From what I've heard from other detailers, used properly they do not leave swirls.
I wouldn't trade mine for anything. It produces far less surface abrasion than any mit or sponge and reasonably won't agitate stuck on mud, goo, or roadkill. It does work very well as an every day or every week washing tool. I put mine on a standard pole. A lot less stooping, bending, and getting my belly wet, especially in the cold weather.
I'm of the opinion that any washing tool will leave some swirl. One can only minimize it. IHMO, a good boar's hair brush does less damange than a mit.