I had a no-peep up until this past Elk season.

As someone said if they move any amout they are off the mark.
I was hunting on foot and off horse back. A bow gets knocked around a bit even in a quality scabbard type bow hold/case on horse back. When I went to draw back and alined the no-peep for my shot at the 6x6, I could just tell it was off. I resorted back to my anchor point and string to the nose, set the pin and scored on my Elk. A couple of days later I tried to shoot using the no-peep. It had moved and was way off the mark.
When I set it up it was dead nuts and I used lock tight on all the screws. Just to much chance of it moving so it came off my bow.
I went back to a string peep with a larger aperture with an amber insert for low light and it's working great.

Im not knocking the no-peep but it just does work for me becuse I move around to much and my bow take a beating at times.