If you have ever gone to a BR-50 shoot, you will see these ugly shower heads on most of the rifles there. If they did not work do you think all those people would spend all that money to make their rifles look ugly. I will say this they have to be put on and adjusted, most of the Sims seem to have the best effect near the muzzle(1 to 6 inches). If your rifle will not consistently shoot under .300" you will probably see much of a difference so on a hunting rifle not a great idea, but if it's first or 5th place then yes.
Len