it is not overpowerd I think, it is indeed the most powerfull armor/robe a mage can get in the game... but you need serious cash to get him.. or if you have TDD installed you can get it from a particular treasure chest in one of the few dungeons
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it is ofcorse your opionen if it is overpowerd... I always use it... it's a really good item... use it and see why people all talk about it