Really good against defensive decks since it allows any of your monster equipped with this to be able to deal piercing damage.
It comes with no attack increase, unlike the other spell cards.
Being able to do piercing allows for some combo potentials like using Mystic Box on Stray Lambs to deal as good as a direct damage, or use Metalmorph for increased damage. Micro Ray can mean a direct attack as well.
That happened to me. Fairy Meteoe Crush on my Red Eye Slash Dragon, I attacked and loss because I took the damage, not the opponent. Card text reads:
“If the equipped monster attacks a Defense Position Monster, inflict piercing battle damage to your opponent.” Who ever controls the card, inflicts damage to the opponent, regardless which monster it’s equips to.