This technique was never taught by Imrich Lichtenfeld and Eli Avikzar because the knife can slide pass the elbow when you try to catch the opponent’s arm in your armpit and the blade can reach your body.
If the student in the attacker role is not submitting to the defense and is retracting his arm in the same position for an additional stomach thrust resisting any forces implied upon, then there is no way this type of arm bar can be applied.
The problem is during demonstration that students are being submissive out of fear to get hurt by their instructors, or training partner, and if they got hit good and lost their ability to recoup and attack again, then any follow up pose will work. But if they did not then this technique is suicidal.
For instinctive defense you put your forearm 90 degrees toward the opponent’s wrist so the stabbing hand will not slide forward and stab you elsewhere and you simultaneously deliver a strike to the opponent’s face to break his train of thought and prevent him to retract and stab again in a slightly different angle.
If you see him coming with an under grip from a distance, you dip with the mirror side of the body forward putting your elbow at 90 degrees diagonally. That will cause the attacker's wrist to slide diagonally from over your elbow to your waiting palm and fingers hook as you do a taesabaki to his dead side. As you hold his wrist, your free hand is punching him in the face once or several times if needed to disorient him. From there you your punching hand join gripping his knife holding hand on his fist. As you pull his arm with both hands, you twist your torso and throw your front leg backwards while lifting your rear leg that becomes the front leg executing a groin kick. That twist and leg switch create kicking distance pulling his arm taking him off balance for the kick. If you did not take him off balance and he pulls his arm while you kick, it forces your foot down before you completed the kick.
If you were already standing closer to his live side, then you do an instinctive defense with the front hand, switch your hands to grip on his wrist and continue with your front hand with a knife hand strike to his carotid artery.
From there you swing the knife in front as you switch legs controlling his arm and taking him off balance for a kick. You then peel the knife and you can continue to slash with the knife, if it did not fall out of his hands in earlier stages.
Take a look at the following Youtube Video demonstrating the aforementioned problem