I think that althought the bulletproof locked door on SAA is a good idea, lets be honest, if one was a hijacker, the best time to storm the cockpit would be when the cabin crew bring us our drinks/food. How easy it would be to pull the hostie out the way, and then once the hijacker is inside the cockpit, no one can then enter to help, even if they want to. Bit scary I would say! The best part is no dangerous weapons are required. Who are the cockpit to know the hijacker doesn't have a bomb on board?
The bottom line is that if they want to get in, they will. A cockpit actually needs two doors, like they have in banks. If security is going to be taken seriously, this is what they need to do.