What's the benefit of milling the slide for the sight as apposed to just drilling and tapping it? Is it just so it sits lower?
There are "registration" lugs that are not milled away from the slide. These match up with holes in the sight. Keeps it square/repeatable if you remove it and increases the durability. Much more holding on to the sight than just the threaded screws. Not to mention that the milling gives you a perfectly flat surface to mount the RMR onto. I guess the Glock is pretty darn flat,,, but many pistols aren't. I'll remove my RMR and snap a pic for you.