Items are just that, items. They can be anything from: a coin to a magically enchanted suit of armor. But their are rules for Items to prevent abuse.
1: If an item has magical abilities, it CAN NOT be at mastery level. It has to be weaker then it's original magical counterpart.
2: The more magical items you have, the easier they are to break (They insta-repair after every fight). This prevents people from constantly swapping back and forth between the same magical items and forces the user to be a bit craftier and more resourceful with their items.
3: Magical Items can not "nullify" anything. Otherwise you could just swap between magical armors and never take damage. BUT they can only offer you some resistance to other magics instead of outright negating them. If an armor does infact negate something, then it breaks immediately after negation.