It is a Slide Release!
It is both a slide stop, the internal sear that engages the slide cut, and a slide release, the serrated button on the outside. The button is there for a reason, to release the slide. The only semi-automatic handgun I can think of that has a slide stop with no slide release is a Walther PP/PPK/PPKS. One must pull back the slide to release it. The degree of difficulty to release a slide depends on recoil spring tension, slide stop included angle, and mag spring tension if empty. One could work on those slide stop/release surfaces if you really wanted ease of release, but clumsy alteration might result in too precarious slide hold back or failure to stop the slide. The small control button surfaces on all these small pistols make for stout exertion.