I am going to have to side with those that stated the advice given in the OP is NOT good advice. In my small amount of police experience I noticed that the vast majority of armed robberies never resulted in anyone being shot. Shooting the first chance you get to act during such an encounter increases the odds of someone dying during the encounter. I would add that my experience is quite different regarding someone getting hit and firing back. I have seen someone manage to squeeze off rounds even after being hit on multiple occasions.
I am always a little bit torn regarding how to react to a robbery though. About the only thing I can say for certain is play it by ear and react to your specific situation. If it seems like giving them the money will cause them to leave without harming anyone d it. If they give you reason to believe they are going to harm someone anyway then fight back. The most important thing is to stay calm and react with forethought and planning.
"Laugh all you want, but when the zombies come we both know whose house you will be running to for protection."
- My response to friends that laugh at me for collecting firearms