Use a false grip for benching in a PL competition and get disqualified. No mixed grip on deads? Dude do you even lift? If you do you suck. Watch any big lifter, they all use mixed grip. I'm no expert but I did pull 545 lb on a rack pull yesterday, with a mixed grip of course. Dumb advice all around IMO, that said, if you don't already know give it a try and see for yourself it's wrong.