Tom Givens taught this technique at the PS Winter Conference in Memphis this past February. I like it a lot. You can keep the gun at low ready while searching, thus not sweeping everyone you light up. The gun can be brought to bear in quick order, and the light nicely lights up the sights. As your head turns, the neck index causes the light to point where you are looking. Pretty slick. The one drawback that I see is that bad guys tend to shoot at the light. You might want neck armor.

Bob Carr