Never use it. Im not much of a ground hunter, but in the trees I usually set up in, I've never had an issue. Even when deer pick up my silhouette and look at me, as long as I don't move, I've never had a deer spook from looking at my unpainted face.
On a cold morning once, I held my breath when a buck looked up because frozen mud fell from my boot. He just kinda hung there, not spooked but curious. I finally had to breath and a big cloud of vapor exhaled. He didn't like that.
Instantly booked.