There's very few emergencies that the lock would kill them in if used properly. Since it would only be locked once the shuttle got to space and once it would open to hard vacuum. It would be unlocked before reentry. The only other failure modes that I could think of would be if the lock was unable to be opened or the key was lost. Neither would be the end of the world, as they would have had tools available to cut or remove the lock.

Given that, I'd push for the lock to be part of standard procedure. It can't be a point of distress if it's standard procedure instead of a judgement call by the captain.