I would NOT dip that feather duster. Dusters are inverts, NOT corals! It will die a very painful death! I accidentally dipped a coral in Revive coral dip and it had a small bristle star on the underside of it... When I realized it was in there, it was too late. It was writhing in pain and its little sides exploded out.
don't dip the duster.
It's not true that you don't have to... it's just very hard to QT them because they can't be kept in a system with Copper. (It will kill their food source.) If you are concerned about ich or other clinging parasites, you could quickly freshwater dip the fish in RODI water. This will stress the fish, so do it quickly, I would say just a minute and it will cause any parasites to burst.