I agree with my friend, Pete. While introducing my neighbor, 67, to pistol shooting, out of curiosity he tried my merit. He ordered one the next day.
To add to Pete's comments, the merit works best for me (I have some some retina damage) on brighter days when I can dial it down -- I can focus on more than just the front sight. On overcast days it isn't as effective. Also, take care not to let it get away from you. The suction cup model is small and easy to misplace. I don't know how many times I've seen a "Lost: Merit device" in the gun club newsletter. For rifle work, I'd opt for the Merit adjustable receiver sight aperture.