The thumbs vs. thumbless thing should be over on the bodybuilding section...... show me a big powerlifter who competes open grip.
Even with thumbs on the bar accidents can happen, just in the last 3 months 2 guys have died from the bench bar breaking free at arms length and crushing something, one at a meet ( look it up on youtube yourself, I'm not watching it again)..... I can see maybe in training with lighter weights if you have an injury, but it's a weaker grip that forges you to cock your wrist back to give the bar a place to sit. Wrap your wrist tight, high up on to the hand and keep everything in line.