I have two monster EO hermits - besides knocking frags off their "perch", they haven't done anything to harm any fish or inverts. The LH hermits we got from Sam are also getting HUGE at a very quick rate...out of all the hermits we got from Sam, only three of the little buggers were caught munching on a coral - they got relocated to our 'fuge at first, but now inhabit the QT tank. Best suggestion I can make is to have plenty of empty shells in your display in varying sizes so when the hermits get ready to upgrade their "house" they have something readily availb. ;)
BTW, our LH hermits are awesome at cleaning!

Wendy