Like Lee, I used them when Wisconsin was a non magnification state for muzzleloaders. We are now able to use scopes. But at the time I thought it would be a good alternative to open sights. One the range during the light of day, they worked fine. Mounted as you would a scope, so you get the full benefit of the field of view. At dusk and early morning, when light is faded.. don't hunt anywhere there is shadows.. you will not be able to see into them. Also the dot in my case (Bushnell Trophy Red dot) grows a tail.
I still have one mounted on a Ruger 44 Redhawk, but that is my fun range revolver. And in that case, it works fine. I disliked the reddots on muzzleloaders so bad, I removed them and went to 1x scopes.