I agree with Ausie-guy. The TIMBERLINE No-peep teaches and consistently allows the same anchor point time and again. Think of it this way - as soon as you were off that anchor (say, shooting up/down at a severe angle and didn't bend at the waist but instead lowered your arm) your anchor point would change right? Now imagine something mounted solidly on your riser pointing back at your eye. The moment your anchor changed, you would see it. Even the slightest change in arm geometry with relation to your trunk is enough to have an effect on the eye/sight relationship. But because the No-peep ensures that your eye is in the same spot relative to the sights EVERY time, you can be sure of a solid anchor. As far as the glasses, you are no longer trying to see through a small hole that can reduce light and images entering your eye.

The biggest stumbling block is that people that try them and don't like them, usually don't give them a serious adjustment period to get used to them. Take a lifelong finger shooter, and get him to convert to a release and you may get the same result - they may not like it.

Jim.