There's is another reason to use the slide release...by always using the slingshot method you turn a handgun into a "handsgun".
In the classes I have run can't tell you the number of times I've seen students doing a one handed disabled reload during a blind scenario either stare at the gun for a second before realizing they need to use the slide stop or try to slingshot the slide with part of their body/clothing trying to catch the rear sight... The last one who did it last summer I asked, why didn't just use the slide release... He realized then he was so ingrained in using the slingshot method he didn't even remember it was there....
When I do a lockback reload at speed, my primary hand never changes grip. When the mag is slammed home with the support hand, as it rolls up into the support grip the left thumb simply pushes down on the on the release. And I start shooting. I teach "slingshot" as method #3, not #1.
The Israelis teach a slingshot reload because it flows naturally with their carrying with an empty chamber method...
From what I saw the SIG Academy was the first to start teaching slingshot...why, because their slide release button is so small and ergonomically out of place it is easily missed by many people. Same with Glocks.
