Good video!
Fighting with a guy who have knife is one of the scariest things that you can do, of course if you fight with the guy who REALLY wants to stab you.
And lot of people do not have what it takes to stab someone, it requires some kind of attitude or mind to do that.
Traditionally here people use knives pretty much in fights, there is something traditional in that, and also reason for that is because laws about guns, so knives are something that everyone can have.
And another funny fact is that most of the knife fights here are happening with simple kitchen knives, or knives for meat or similar.

When guy pull knife on you, and approach closer then 5-6 meters you either run or put him down ( having gun make sense, and yea, I suggest that you put him down ).
Yea, I have seen some knife fights, and there is maybe (probably) effective technique for defense against knife, but having gun ready is best for me.