Brad in answer to your question, I think they help in certain situations. A yote or cat my come running in if they see the decoy, or they may sit back and watch awhile, as usual you can't perdict what those critters might do.
I think Byron Souths video shows a decoy is useful and the new jack in the box by foxpro seems to be working well for those that have tried it out.
I think it would be useful in heavy cover for cats to keep their attention on the decoy instead of looking around and seeing you nearby.
Kinda like those who use an ecaller and put it out in front of them and directs the predators attention away from them, where hand calling the predator will be looking at you and you have to remain motionless.
As many have said the predator is looking for what is crying and they see what's crying is moving. LUNCH TIME!!! /ubbthreads/images/graemlins/wink.gif