They shouldn’t need it in a hurry. The cockpit doors are strongly reinforced and always closed and locked now during flight.
Not true, I've personally seen them open so that the pilot could answer a call of nature. They would block the aisle in front of the door with a beverage cart. But apparently that, when the cockpit is most vulnerable, is one of the times when the federal powers that be insist that the gun be locked up in that chastity holster.