Your results alone are a far cry form what is required to refute the value of the CD's. More people having tried need to come forward indicating results of using them.
I have seen it less than a dozen times myself over many years. Best evidence I have is that losses of chicks and hens to smaller hawks is greatly reduced when adult rooster is present. Such roosters may not always be as a effective against red-tailed but even then losses still reduced. Dogs...
I do very well against Coopers Hawks using full adult standard size roosters. In your setup, more than one may be better. All bets are off if your "Coopers" turns out to be a Goshawk which does have similar feathers and may be in your neck of woods. If latter, then cover run. I also have...