I know this is getting a lot of grief, but I kinda see the attraction.
MANY guns, including the M16 I carried in the Marine reserves years ago, have a safety that functions by preventing someone from manually and deliberately pulling the trigger.
Now, YOU may not think your Glock needs one, and that's fine... but if you are gonna say it's pointless and dumb, I'd say you are flying the in the face of 120 years or more of war-fighting practice.
SOME people (apparently including a lotta people who determine how the guns our in military should work) WANT an "oops, I should not have had my finger on the trigger" type of safety.
And that's fine by me.
Not looking to give anyone grief, but my perspective is that external safeties are primarily intended to prevent the trigger from being actuated by something other than your finger - which is either on or off the trigger. And once your finger is on the trigger, the safety is irrelevant, unless maybe you use it for gripping advantage.
I find slide safeties on pistols to be very awkward, possibly somewhat because I learned on Glocks, but I think also they just don't suit me biomechanically. I want my thumb below the position where I could actuate a safety immediately on draw contact. This isn't an issue with long guns.
The only pistols I have with slide safeties are rimfire, which are shot from low ready, and the safety is disengaged off the clock. Obviously not everyone thinks this way, and there are plenty of open, limited, SS, etc. shooters who can draw and shoot just fine with a slide safety.
Part of the Glock design involves establishing a minimum trigger weight that's considered objectively safe without a slide safety. If I were going to consider a gun with a slide safety, I would at least want a much better trigger out of the deal. Even the DA triggers in my DA/SA guns are under #4, and way smoother than most OE-ish Glock triggers.
From my standpoint, a Glock with a slide safety is a stick with two short ends. I have flat safeties on my DA/SA guns, so they are basically just pins. They never perform a safety function either objectively or per rules.
I would agree that a hot gun with a slide safety being thrown around in a grappling, etc. situation is safer than a hot gun with only a heavier trigger - assuming the shooter was able to get it back on safe before losing control of it.