If the mind fails then it does not matter how many mechanical safeties you have present. If you trust that mechanical safety then the mind has already failed you. I won't carry a gun for self defense that has a manual safety. It's one more thing that can break or go wrong at the wrong time. I carry a sig 220 and often a revolver back up. No manual safety on either one. Neither has "gone off" with out me pulling the trigger. I keep my home defense shotgun and 45 carbines safeties on as they are not holstered and in my immediate possession. I don't need to draw and fire them as quickly as possible to protect my life.
The mechanical safety only provides the illusion of safety.