We used to call those a "Quick Stop" because they apply pressure to the chin bone. I've used them a couple of times teaching an OTTB what whoa means and to re-train their thinking that a tighter rein means go faster. I always put it on so that the bar hit right behind the bump of the lower lip, right over the bone. Not too tight around the nose and I used a separate set of reins from my bridle reins because essentially, I used it like a 2 rein set up. I've never used one as a sole piece of daily tack and I haven't needed to use one in over 20 years, so no pics either.