Bullpuckey. Glocks don't have an external operator-controlled safety, but they do have redundant internal mechanical safeties.
"Safe Action" System
The "Safe Action" system consists of three (3) automatic independently operating mechanical safeties which are sequentially disengaged when pulling the trigger and which are automatically re-engaged when releasing the trigger.
Without actuating the trigger it is not possible that a shot is fired.
The revolutionary trigger system consists of:
Firing pin safety
Furthermore the "Safe Action" system provides a constant trigger pull weight and a constant trigger travel from the first shot up to the last shot. GLOCK pistols are safe when dropped, when they receive any other abnormal shocks and are fully functional at temperatures from -40° to +70° Celsius.
The GLOCK "Safe Action" system has revolutionized the handgun industry and has been widely adopted by law enforcement and other official users as well as commercial and competition/combat shooting areas due to its simple, fast, safe and reliable application.
The main advantage of the GLOCK "Safe Action" system is that is has no external safeties. Because of this, the user can fully concentrate on the tactical tasks required whilst being in a stress situation and does not need to think about any safeties to be deactivated.
None of which can be "engaged" or "disengaged" in any manner meaningful to clearing the weapon. Point of order sustained. If you want to get technical, the M1911 and Hi-Power have several "safeties". Most, however, like the Glock's "safeties", are irrelevant to clearing the weapon. (Hi-Power has a magazine disconnect.)
The only people I've ever encountered who have problems with DA/SA transitions are people who lack an understanding of the fundamentals of trigger control, frankly.