^
flipping all your opponent's face-down monster into face-up attack position means your opponent is now susceptible to battle damage, plus, no effect activated means if your opponent sets a Flip monster, you won't get punished for flipping it face-up.
Like the OP said, too many resources for a mild effect at best. Barring specific decks like Subterror, not many players put more than one monster facedown at once.
Anoymous
