With charges for a very high level Iron Golem together with Iron Maiden, Metalgrid lives up to its name by cursing enemies to receive quite a bit of damage they inflict back. Defensively, Metalgrid is useful too, bestowing potentially the best increase to Resistances and Defense out of any amulet in the game. It also offers an extremely large flat attack rating boost.
However, since the level required to wear Metalgrid is very high, players are nearly guaranteed to be in Hell Difficulty by the time they can wear it. The Iron Golem summoned is very frail when pitted against the opponents found in Hell, especially considering it cannot benefit from the various skills and synergies Necromancers have, so it is of limited value. Iron Maiden is likely to not be useful either, given that all enemies in Hell have very high physical resistances and large health pools compared to their damage output.