I have been using Pigeon decoys intermittently over the past few years. I've noticed they dont not really work for pigeon, because they are too smart and are not tricked by them.
But, what they are good at are attracting other species. Often starling will fly down quicker if they don't take a good look. Grackle will be easly tricked and fly down quick, but in most situations you cant shoot (unless your farm has permit). I've noticed having a few Grackle eating grain will lure more Starling and Sparrow. It will make for an action back few hours.