This, like the Armory counterpart, brings up the question of slot-targeting. If you have two weapon slots or two shield slots, and neither is empty, the player will have to select a slot to replace.
Also, while the shield variant does bring added flexibility, the presence of Animate Weapon in the game makes this card redundant. He may have inspired one of the Armory's better cards, but that is as far as wizelsnarf got - I can't see a way to make this card work. I didn't know about his idea or the fact that he inspired Dual Shield, but Dual Shield has made me think of this very card before, and I dismissed it right away as impracticable.
The art's nice, though!