A lot of people go the route of the adaptor - where you remove the rear sight, install the adaptor in the dovetail and mount the red dot to the adaptor. People do that for self defense/carry and for competition. It works. Just like a scope on a rifle. The higher the optic is from the bore closer you'll have to be on knowing where to aim to have the bullets hit where you want them to hit. The bigger than distance between the bore and optic the bigger the distance will be between point of aim and point of impact than a pistol with the milled slide at the same distances to the target. There will be one spot where the bullet hits right where the dot is on the target. At other distances to the target the space between point of aim and point of impact will be greater and you'll want to know that to compensate in your aim (true for the milled slides, too, they just won't be as far apart between aiming spot and the bullet impact spot.) This is a fairly cheap way to see if you like the dot optics on your pistol. Many love it, many don't. If you decide you don't then it's easy to remove the optic and adaptor and reinstall the rear sight and no one can tell.
You don't have back iron sights as the red dot+adaptor mounted high up on the slide take the rear iron sight dovetail and the front sight is too low to use. Some people will say you don't need the back up iron sights. Some people will say you do.
There are companies that will mill your slide so you can mount the red dot to the slide. Make sure of what you're asking for. Not all dot optics have the same "foot print." That means that length and width of the body may be different and the two holes for the mounting screws may be in different places in the cut milled into the slide.
Some places will mill for a specific foot print which may mean you can run different red dots - but they all have to have the same foot print. Some places may mill the slide in a manner that allows the use of adaptor plates between the slide and dot optic. This allows you to choose between different plates that then allow different dot optics.
Do some homework, ask folks here about their experiences with different vendors and different methods of mounting a dot optic to their pistol slide they had milled. And where/who did the work.
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