I had one on my first M4. It was a cheapy that I got at a gun show, 40mm. I even took my front site off, thinking it would be really cool to use the red-dot, but I hated it. I can put a gun, especially airsoft, into my shoulder, and get what I want without any sights. I cant imagine trying to use a little 20mm (ish) red-dot on a mac or a scorpion. I see them on shotugns too, which is just wrong.