2.65 million people are reported to use a firearm each year in self-defense. Perhaps 2,650 actually shoot. How many of them, using a device which prevents the firearm's use if forgotten, will die by their attacker should they fail to remember the device is in the gun? Again, this is a device to be remembered whose purpose is to prevent an accident from failing to remember something else. Not very smart.
If one can remember to keep loaded firearms away from children, they do not need to remember to remove your device later when they need to shoot.