This is Holosun HE507C-GR, a green dot. I see a green dot better than a red dot, and while I am red-green-brown colorblind, I have read that this can also be true for people who see color. The 2 MOA dot can be switched among the 2 MOA dot, a 32 MOA circle, or a combined circle dot.
For target shooting or distance, from what I have read, a 2 MOA dot is generally preferred whereas for self defense, quick acquisition, shooting 25 yards or less, generally 6 MOA.
On my Ruger MKIV, I removed the front and rear iron sights, and mounted it using a Farrowtech plate that mounts into the dovetail for the rear sight.
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One interesting thing I learned is that if shooting the dot, I see it better with my regular glasses than with my prescription shooting glasses which have my dominant right eye focussed on my front sight. This is because with a dot you only need to focus on the target, one focal plane, as I understand it.
I am considering putting a dot on one of my SD and training guns, as most instructors and guys I train with seem to do nowadays, but haven't made up my mind about whether I want to try it or not.