The way in which they are functionally deficient is that they put different amounts of pressure on the barrel in different directions depending upon the day, how you're shooting (meaning from what position/support/tree branch/whatever), and the alignment of the planets or something. That can push POI around on you, sometimes surprisingly far. Or at least, it has pushed it around on me and on my brother, many times. On a given rifle, and for a given hunter, it may or may not push POI around to harm your hunting.