Our experience was definately on the negative side ...
We had three peppermint shrimp in a 72 gallon, and they eventually cleared the tank of all fan worms. In addition, a nice Hawaiian feather duster bit the dust with the shrimp sticking their claws into the tube.
The shrimp were also caught several times with margarita snail meat in their grasp. Stomatella snails (and a lettuce nudibranch) also perished, whereas ceriths and turbos were safe.
As far as aiptaisia, the shrimp performance varied ... depending on how much fish food they were able to snag ... when they were hungry, small aptasia's were targeted, otherwise, not.
We've found that they will do well clearing aptasia if they have no other source of food.