The reason they are so much faster is the surface area, with the orginal clay bars falling well short of the area of a clay towels surface, that is about 6 times larger (as you can see in the image with the yellow clay bar on a towel on the right).

Since we first got them a couple of years ago, we have found them a lot faster and easier to use, in fact it's now a rare occasion we ever go back to using the clay bars anymore.