I would absolutely agree that knife defences are useful for that reason, a lot of guys with knives like this guy are idiots and knife defence skills are useful against these guys, but you dont even need to be a badass high level silat practitioner, an average guy with some basic rudimentary knife skills and who is really set on hurting or killing you is going to cut/stab you regardless of how well trained you are. Most I can say about how useful knife defences are against a basic knowledge, determined knifeman is that you might be able to take them out after they have stabbed you repeatedly so you more likely to be able to enjoy the privilage of dying in hospital later rather than on the street there and then. Maybe.
And that's why you don't wait to find out how much skill the blade guy has ...
If confronted with a knife .... shoot as fast as you can.
The American martial art .. “way of the gun” can be an effective defense ... but only if your ready, fast, willing to take a hit and do the deed.
One of the worst attacks is a trained blade guy with a real goal.
Situational awareness is key .. and really the only defense. (you must be a blade guy)