Yes, the troll armor is really nice for something like a Great Sage, I think. This does work on pretenders, I've had success with it in MP.
One other thing: if you give the Amulet to a unit with more than two misc slots, and the Amulet is in the first misc slot, then the Amulet will disappear when the unit changes into a Skinshifter.
But because of the age issue K pointed out, it's not a good plan to do this to a Crone, for example. And I'm not sure if the amulet works on pretenders at all (in regard to changing them into a Skinshifter, it still berserks them). I tested the Amulet with an Oracle, and after 200 turns, the Oracle was still an Oracle.
Here's my Great Sage troll:
