Nothing but great marketing and more than not, a gimmick. I can reproduce the same sound on several calls I already own and so could many of you if you try. Again, good marketing however in my 24 years of bowhunting, never once heard a buck do it. I will admit to turning a buck around from 250 yards with it last year on my River Valley Deer Flute. At the time, I didn't realize it was a " buck growl"....I just wanted his attention when he didn't respond to my grunts.