I've got a little experience using one. As others posting have mentioned sod and even damp earth will clump up and hold the rocks in the bucket unless you shake like crazy, which is inefficient and will punish all of your loader wear points. Really, something like a power rake or rotadairon is needed for finish landscaping.
Still, not wanting to bend over and pick up a lot of rocks, especially the heavier ones, I had one built by a local welder using a worn out bucket for fraction of the cost (about $400). The spacing is wide: about 6". I found the best way to use it is with the bucket angled about 30-45*, drive forward and comb the rocks out of the soil. I rarely lift and shake anymore.