Avg Glock trigger pull is approximately 6.5lbs +- That is the equal and opposite "tipping point" force your thumb must contain: holding the gizmo down. Pressure needed to overcome common friction/lock in for a retention holster could easily equal 6.5 lbs. With the trigger obstructed, the gizmo should try to move back (protrude): can you differentiate static resistance from the holster verses gizmo trying to move under your thumb and recognize it every time? A person could hold 20+ lbs of pressure on the gizmo then release slowly trying to determine if it starts to move as pressure is reduced? Maybe you can if you focus your attention on it each and every time. But the gizmos selling point is preventing NDs when your not paying attention isn't it!
Please understand the "Disclaimer" in the sales pitch: adds an additional layer of safety. You must still follow what is required in the "other layers of safety", It doesn't say you can ignore them. I went to TAUDEVGROUP and searched for SDC operating instructions, instructions, how to use SCD, SCD usage: nothing! Only the sales pitch narrative and "Gunsmith installation required". So, thumb on gizmo, jam in holster and release!
The unanswered question remains: If there is obstruction pressure on the trigger and the gizmo is released: will the gun fire? YES! Reliance on a device that gives a false sense of safety is dangerous. Following firearm and holster manufactures procedures negates any justification for spending $80 on a gizmo that will reinforce sloppy complacency. Sooner or later; somebody is going to rely on it too much, perforate something and file a Lawsuit on the gismo. I'm not trying to be adversarial, I'm just supporting proper procedures above what I believe is an unnecessary accessory. IMHO
We are adults (Ayoob included) with different opinions and principals. Its solely you Choice. Hope it works out.
Very good points and part of doubt or question of the device is it a reliable device. That was initial question and still is. Most of this discussion did not answer the OP.
Anytime something goes in the back of glock slide one needs to be careful. There are special slide cover devices for example that turn a glock into a select fire weapons.
I have not found any cases of failure without so far except for adverse conditions.
The question was raised about just how well does it block the trigger. It was really questions like these I was looking for answers to. I got no information from anyone that has tried it or even knew any that had.
On the basis of Ayood's opinion I will test it. Just how much pressure do you need to exert on the device with your thumb to block a 'pull' on the trigger? I would put it on one of my glocks, find a fixed peg or spike, put it in the trigger guard and push the gun forward. See just well that works. See if it a viable solution or not. I have almost decided to order one and test it.
I would not it use on a carry gun until I was satisfied with its function.