Well, since it said drummer, I gave it to him as a drum, since that's where that bard's proficiency lies. It's too late there - if I try to take the item back, the player would feel cheated. Also, he has over a +15 on his perform check, so it's automatic for him. And, it doesn't say that it takes effect one round afterwards like the bard's other special abilities.
Another question: on the monster side, a vampire has +4 turn resistance. Would the +4 turn resistance from the cloak of turn resistance stack with that to give the vampire +8 to his turn resistance? I think it would, since it's an unnamed bonus.