I have heard of peppermint shrimp shreading the "feathers" of dusters but never seen it in person. What both my cleaners and my pepp shrimp like to do is "clean" the feathers, for food possibly, although dusters eat such small particles, it could just be because the shrimp are bored

LOL
I'd say go for the peppermints, they might eat a duster to two but getting rid of the aiptasia is the primary concern. FWIW, the "mini-duster" population in my tank kind of runs in cycles anyway. I'll have a bunch, some will die back and then in a few weeks, I'll have a large population again.
Alice