Sure you can use the grass between your thumb method, but you will never know what it sounds like before you tried with that grass. Those who have tried that knows that problem. With this call you can tune it and it stays like that. You cant do that with a piece of grass. The grass will also tear apart after a few blows. You can even make two or more overpieces with different tunings in this one, and it will still be lighter than most modern calls for predators. Why was this call invented? Because the grass between your thumbs are better?
And yes, as the decription says it is a primitive style call for those who like it that way. If you tried it before placing a comment, then you will understand. Also, made out of bone, or laquered wood (as many modern calls are) and plastic for a reed, it lasts at least our lifetime. Wheather doesnt effect it, but it sure does to many modern calls. Saliva freezes in them.
This one can easily be made entirely out of plastic also. Maybe its not popular with a good call that can be tuned in many ways, and that anyone can make on their own..?