They are a flock in the pocket, kind of a call. You can move up or down the tongue about a 1/16" and get a completely different bird sound out of it, and then you can change the pressure you play it with and the sound changes again, and then you can thomb the tongue and it changes the sound in the call completely again. If you played the exact same spot on the tongue, you can get 3-5 different birds without ever lifting the striker.
Not sure how these calls ever passed turkey hunters by without someone knowing about them, or some call co. picking them up and selling them off the shelf too hunters? Most guys have never heard of or seen one.