It's too expensive. Counters are cheaper than the cards they counter, and this really isn't that good of a counter in the first place. I'd drop it as low as 4/3 since it just borrows a creature for 2 out of 4 turns. (I assume the switching occurs right after the creature attacks, not when you use the card on the creature.)
Nvm, didn't take the fact that it's also like a 2-turn delay/freeze. What happens if the opponent's field is full when your creature is supposed to move to your opponent's side?