Many of the knife defence techniques I have seen are disarming methods. Some are simple and practical and others are fancy. Though theoretically they may work in some situation, but what is important is to teach the students to judge carefully which comes first: Disarm, Strike or Take-Down? But honestly, if I have all the chance to run away I'd do it :-)
Disarming a knife is a tricky matter. In fact, if done incorrectly, it could cause injury or death to the defending individual rather than a life-saving technique. Surely we don't want to be locked in a physical bloody struggle where both could get killed. The emotions and tensions are high and timing and senses to defend could be badly affected. Chances are the attacked could get killed. In fact, I have heard known martial artists in the Philippines who got killed in knife fights because of failed techniques against a non-martial artist attacker.
I did put some disarming techniques to the test and sparred with some experienced knife-based martial artists. Some of knife fighting disarming skills went fine during preemptive strikes done in a slower pace but as the attacks went faster and faster at varying angles, none of the techniques worked anymore. I had to shift from one technique to the next but it was difficult. As the adrenalin level went up, my timing was affected. I had to rely on my evasion, parrying and striking skills. Obviously, I did get some supposedly bad "arm cuts and stabs" from the aluminum training knives, but what saved me were the empty hand strikes that went in so neatly to the faces, jaws, groin, legs, neck, eyes and arms of my sparring partners (I have posted a clip of the striking patterns in my videos).
As an instructor, I always tell my students to focus on striking rather than disarming. Fatal strikes to the eyes (face or neck) with the help of evasion, parrying and footwork must come first before executing a take down or disarming. The Filipino phrase "Palambutin muna ang karne" or thaw the meat first before eating it must apply first. That is why we destroy the limbs and senses by applying all dirty tactics in order to control and win a fight because in there is no such thing as a fair fight out there in the streets. But often when martial artists practice knife defence, the disarming techniques are the most preferred and safest methods because nobody doesn't want to hurt his or her partner with a painful strike to the face or groin or an eye jab. This makes knife sparring even more difficult because it is hard to apply all the dirty tactics such knuckle or bone breaking techniques. In fact the sparring continues even after one or both have been theoretically "stabbed" to death.
Don't forget the strikes as they will be your best techniques in case of a knife attack. Remember, strikes can easily and fatally be delivered delivered to the most painful parts of the body in a rapid manner with the use of evasion, footwork and parrying skills. I always tell my students to "turn the switch off" by rapidly striking the face, eyes, head and surely the fight pattern will dramatically change to the defender's favor. In fact, this mindset saved one of my student's life in London from a stabbing incident that almost instantly killed him. If you train your hands fast, your hands would even be deadlier with knives. I'd rather see my student survive a knife attack because he picked a stone and hit the attacker's head with it than see him in his own funeral because of a failed disarming technique.