The only thing that a single level retention does (thumb break, serpa button, etc) is keep the gun from falling out when you are running, jumping, climbing trees. They might slow down a bad guy a little bit, so you can put your thumb in his eye. Level two and three add a couple more obstacles to a bad guy, without unduly slowing down the good guy. Ultimately you need to train, train and train some more. The guy who shot himself in the video which spawned all this, states clearly that he switched weapons platforms and holster types, which led to him shooting himself.