Do you mean the California Car Duster (CCD) you can get in a car parts store or Wal-Mart? I find them effective and safe provided you don't use them like a mop and mash against the finish with them. The trick is to barely touch it sweeping in single direction strokes. I shake the duster after each stroke. I've been using them for over 10 years with good results.
The biggest issue I ever had was with initial streaking from the wax in them. I let a new sit on newspaper for several days, rotating it position, before using it. Also, don't use it in the direct, hot sun, the heat will cause the waxes to streak. Other than that, good results.