THUMB SAFETY ON A GLOCK??!!
The more I have run classes and the more we have pushed the edge of the envelope, coming very close to the realities of actual gunfights, the less I think operating a manual thumb safety is an issue. The thumb safety is a different matter than a grip safety. The thumb will be in position to disengage the safety anytime the pistol is gripped. And there are steps to be taken in events where the grip is not perfect. But those are training issues that are easily addressed.
What does it do for you? What is the benefit? Here are a few.
1). An added margin of safety when the pistol is unloaded or loaded.
2). An added margin of safety when the pistol is set on a surface, sans holster, and out of your control.
3). An added margin of safety when holstering - where most self inflicted gunshots occur.
4). An added margin of safety if the weapon is dropped. Yeah...I know...but apparently it happens alot.
5). An added margin of safety when drawing - thumb is usually not in position until cleared of holster and driving forward.
Does it help you kill the bad guy better or faster? No, but neither does it hamper you from doing so as you manage now. In my opinion, after some nearly thirty years teaching gunfighting to gunfighters, as long as something does not detract from mission one, added margins of safety are a good thing.