This thing is great. It works for both dirty water/splattered kind of mud, and the thick stuff that is stuck between the toes. In fact it works really good for the thick stuff because the bristles get in between and scoop it out. You do have to change the water very often; when its really thick, you have to change it before you finish all four paws but it still beats spending ten minutes with three different rags and towels trying to scoop it out.
Changing the water is as simple as rinsing it out a couple times and filling it back up. You can screw off the top, remove the bristles, unroll them and clean everything, but I have found that isn't necessary. It fits together just right so a couple of quick rinses and the dirt all flows out.
Great! Has helped with the nightmare that is muddy winter dog cleaning, very helpful and would recommend.