Great discussion on this thread.
The Glock has a Slide Stop and a Slide Lock. There is no Slide Release. When Glock designed the firearm, it was meant for Military use or a Combat Weapon.
Glock made the Slide Lock lever flat because it was never designed to be used to "Release" the slide. Glock designed it for the Overhand Method. The actual part is called "Slide Lock". As John Payne pointed out, the same process is used for clearing malfunctions and Glock felt it was better to work the slide with the Overhand method.
If you are able to get your hand in front of the barrel using the Overhand method, I suggest you put the gun down and get some serious training.
The Glock also has a "Slide Stop". The two small take down levers used for field stripping or taking down the slide is the "Slide Stop". The reason they call it this is because the part is flat with a hooked edge on one end that Stops the slide when moving forward during the Action sequence.
In closing. The Glock has a Slide Stop and a Slide Lock, but not a Slide Release.
Which method you use is up to you. But if you are going to use the Slide Lock to release the slide, you should get an extended aftermarket versions because the stock part is not designed for this and gives you very little to push down when you perform this operation.
I like to keep my operational functions simple and minimize differences as much as possible. Overhand covers many operations and I choose to operate my Glock as it was designed.