is one of the few methods for knife defense I find sensible if shtf, and its full of irimi spirit.
We should realize there are two points to "reality": 1) What makes reality "reality" is that anything can happen (i.e. Reality is Infinite Possibility); and 2) Since anything can happen, reality is equally marked by the known, the unknown, and the unknowable. Therefore, I think it is a step in the wrong direction to start talking about "reality" by starting to talk about what won't happen in reality.
There are some similarities between what the person in the above linked video has said and some of what I said above. However, we differ in that I do not universalize my experience at the cost of negating what is present in every human vs. human conflict: Fog (i.e. the unknown and the unknowable).
For example, while I may say IF you can run away, you should, I know that there are situations where perhaps you can't run way. This is why I chose to use the word "IF" - because there are times when you can't. For example, if you are attacked by a knife-wielding subject in your home during a home invasion incident and your family is home - running away is not an option; when you are in the military and you've been told to hold a line and combat has entered hand-to-hand range - running away is not an option; when you are a police officer fulfilling your duty and someone else's life is at risk - running away is not an option; when you are cornered and/or in a confined space - running away is not an option; etc. Therefore, while I would say one should run IF possible, I would NEVER go on to say that one NEVER needs to train for closing distances and/or the presence of gaps when defending against a knife because if such a gap should open and/or be present you should ALWAYS run away.
As I said above, in my life, I have been attacked three times by a knife-wielding subject - once as a civilian, and twice on duty. In none of those cases, was I afforded the opportunity to run. However, in all of those cases, a gap was present at the commencement. In one case, I was in a confined space with the opening out of the room on the other side of the attacker. In another case, I was in the process of closing the gap when the attack occurred. In the last case, the weapon was in the process of being drawn and to take advantage of the gap present by disengaging would have allowed that weapon to be drawn fully.
Though these all occurred in real life, I would never say that these make up the whole of reality, and thereby I now only train for when gaps are present in knife attacks. No. I know, and accept, that there is always a fog to combat, and that these examples then are at most just a part of reality - a possible expression of the unknown and the unknowable. Self-defense gurus should stop universalizing what they have faced. Moreover, they should stop identifying reality with what they imagine that would do if they were in the attacker's place. Leave reality to what it is: unknown and unknowable. Denying this is what is most delusional in the self-defense industry.
Techniques, etc., should stop aiming toward a one-to-one matching of self-defense scenario and tactical response. The practice of technique is not about this type of matching. Technique training is about the acquisition of skill sets - skills sets that you may use entirely, combine, bend, warp, deconstruct, modify, negate, partially use, etc., as dictated by the unknown and unknowable of reality. Technique training is not about dealing with reality in any kind of direct fashion, and scenario training can never put an end to the fog of combat. Look then to the acquisition of skill sets in your technique training - my motto. Yes, remain critical, but have that critical mind be constructive in nature.
Thus, when I look at techniques, I'm looking at them from a cost and benefit point of view. I’m interested in the economy of the technique. Thereby, from the onset, I accept the technique as it is presented. Then, I look to see under what circumstances it remains viable (i.e. it does what it is supposed to do), and I look under what circumstances it fails (i.e. it does not do what it is supposed to do). Then, in my practice, and in life applications, I try to keep that given technique within its economic range.
Looking at this technique in this video, I would say it's a good one whenever you are in close and tight AND your two-hand grab is able to maintain a mechanical advantage over the attacker's single arm (holding the knife). However, I am not ever going to say that you will always been in tight when a knife attack comes because you can always run away when you are not in tight.
And, in looking where the given technique may fail, I would note that there are a lot of fog-produced elements that make one unable to maintain the needed mechanical advantage over the suspect's arm once grabbed. For example, some things, things that are unknown and unknowable at the time of practice, and that can take away from your mechanical advantage over the attacker's single arm are: He/she is stronger than you regardless of you having two arms against their one arm; He/she is skilled at generating leverage with their single appendages; He/she is armed with another weapon in their other hand; He/she has an accomplice in the attack; You are on bad footing or wearing bad footwear; etc.
Hence, for me, this technique is best suited for times when you are up close and tight, can't run (for whatever reason), are unarmed yourself, the attacker only has one weapon in one hand, no accomplice is present, you are on good footing, wearing good footwear, the attacker is unskilled at manipulating leverage, and the attacker is close to being weaker than you. When I look at the technique this way, I see that like all techniques it has a very limited practicality. I accept this. This is life. Thus, I can say, it is good for where it is suited, but its far from good enough to stop training in other tactics that equally have a chance to be part of reality.
For me, whenever I see or hear an instructor start talking about reality and what it doesn't consist of, I don't think they've been in many real situations themselves. For me, it's a red flag, and I think it should be one for everyone.