Merlin would make a nice mirror for Harry, I guess.
Presumably if he has it, he didn't use it much. That mirror is already taken by Marcone. No, if it's the Merlin, he got the coin safely, he stashed it in a box without being Shadowed, and he keeps it around for when he needs power more than reason. And when disaster strikes, he will pick up the coin and find out it's one of the thugcoins, and be none the stronger for it (though a bit less killable).