Folks I know that have used them say to use them at the right time, when the bucks are ready for a challenger. (pre-rut?) Rattle, then see if someone shows up. If he's mature, snort wheeze at him. That usually makes them wanna come over and knock your decoy over. Remember, they'll prolly come over and approach him from down wind. If he licks his nose while coming in, he's ready to whoop a$$. On the other hand, I've had times during the rut when you could throw rocks at a buck and not get his attention. LOL
p.s. Spray him with some buck scent and don't get your scent all over him.