I am right hand dominant, and prefer to use my index finger for releasing the magazine. It's an easy swap on Gen4/5 Glocks.
My reload technique is the method described in Shannon Smith's video, except using the index finger instead of the thumb. I still "flip" the gun in my hand and would have to do so even if using my thumb. Those USPSA GMs are fountains of knowledge, and I am always grateful.
During the "flip", my right hand thumb goes high and the distal phlanges of my middle, ring, and pinky fingers move from the side of the frame to the front stap. It feels like a sliding motion. As stated in Shannon's video, I can fit a finger in the space between my right hand and the frame of the gun- most of my grip pressure at that point during the relosd is concentrated on the front and back straps of the gun.
I started out pistol shooting with a USP, and was immediately using my index finger on the paddle. When I then started shooting 1911s and getting into competition shooting, I was initially concerned by how much I had to break my grip to "flip" the gun to hit the mag release, but my worries were soon addressed when I saw that much more advanced shooters than myself "flipped" the gun for their reloads and had great results.