Dovetail plates that allow a user to mount a miniature red dot sight to a pistol's slide have been around for a while. Traditionally, these plates have been a flat adapter for a particular optic, but they were inherently difficult to use due to the lack of an iron-sight reference to help locate the dot during presentations and nonstatic shooting.
Barry Dueck, former U.S. Marine-turned-competitive shooter is also the head of SureFire's Suppressor Division. He created an advanced mounting plate called the Red Dot Back Up (RBU). What's unique about the RBU is that it integrates fixed iron sights into the base plate that replaces the rear sight. There are specific RBUs available for most Glock and Smith & Wesson M&P pistols. Different models are available including a multiple-fit version that hosts most available mini red dot sights.
A sight pusher (or hammer and punch) are all that's needed to install an RBU. Dueck Defense provides an Allen wrench for a set screw. The RBU goes on like any aftermarket rear sight, while a set screw offers additional security. Simply center the RBU in the dovetail, mount and then zero both the iron sight and optic. The iron sight will be visible in the center of the optic's lens (or in the lower third) as a reference or as a backup in case of optic failure. My preferred RBU is for use with a Leupold DeltaPoint Pro, due to the DeltaPoint's optionally integrated and adjustable rear sight.
In mid-September, I observed two new female shooters during a class at the SIG Sauer Academy. The first half was spent working on fundamentals using iron sights. The second half was with a pistol-mounted red dot. Their improvement not only surprised me, but also the instructor who said, "Their shooting is simply incredible." We observed the two shoot a walk-back drill from 5 to 25 yards, keeping all but a handful of rounds in the center 8-inch circle of the target. Those outside the circle were within a couple of inches.
If you're undecided about modifying your pistol, the RBU is a fine way to test the water.