How good would Metagross and Mega Metagross be if they were given just a new move in the form of shift gear?

Like we know Metagross doesn't have any good setup moves like other pseudo legendaries.

Dragonite, Salemence,Garchomp have Dragon Dance and I have no idea about the others.

So how good would Metagross and Mega Metagross become if they were given shift gear just this one move?