Cute but there are several flaws with this video.
They are actors and know what is coming. In an actual extreme encounter, there are so many variables that one would be hard pressed to even begin to list them. And chances are pretty good that a victim is not going to see an attack coming from its inception; its very beginning.
They are not using real weapons. This and because of the fact that they are actors and know that neither one of them is going to get injured, means that they are free to respond quickly for the camera. In reality, not only might a victim be caught off guard, but there is also the introduction of the questioning/hesitation of one's reaction to a violent attack. Most people, when faced with something like this in the sudden extreme, take a moment or so to gather their wits and initiate a response. Even well trained people evaluate a situation before responding with force simply because they naturally will attempt to gather information both for delivering fire and surviving the encounter.
What this means is that your firearm needs to be ready for immediate use and in a position where you can get to it as quickly as possible. Time and distance are your friends along with cover and where needed, concealment. However, these are ideal conditions and are not likely to exist in the all together if and when an attack comes.