Yet my question "Does the burying of 1 card until PC is used worth the additional deck order swapping code?" remains for people to answer.
Also the current wording indicates the 2 copies would nullify all their effects.
I assume either
a) you mean playing 2 of these would cancel the effect
or b) the wording makes it sound as if the effect is canceled every other turn.
to answer
a) Non-stackable, 1 played flips the deck, so long as the card is on the field, deck stays flipped.
b) refer to a.
When the card is destroyed, the deck returns to normal.