Well this card is just used to make sure the Two of Coins mobs will not aggro or attack you unless you attack them. It is good for leveling low level jobs, but after lvl 7 or so, no need to keep this when two lvl 5's will be easy pickings.
I'm not SURE about this, but here goes: I think that if you're carrying the card, then the Two of Coins will no longer aggro you. I think it works the same for all the Cardian monsters. But I could be wrong.