Exactly, the dropper will only send the location after he has left. As long as the dropper does not use the same location twice he will be totally safe. This will not always be the case with the mail, I would suspect that when mail regulations require ID and going into the post office for most mail then this idea will be a lot more useful. This would be good for IRL dealers except for the fact that they need to be paid, if the client is using bitcoin to pay him then why not make it totally anonymous in the first place.