I have never heard of these but it sure shares a similarity with my setup. The cutting tool as well as the adjustment screw are the same.
question:
How do you think you are going to save weight by cutting off 4" of the barrel, and then permanently attaching a barrel extension?
clay
while I do agree that it will move it back a bit, I don't think you will realize that much difference.
but, I do think it will look cool