I haven't been studying karate for very long, but both of the techniques in the videos differ from what I have learned for knife defenses. The defense I have a learned against a thrusting knife attack like in the first video starts with a twist to escape the thrust and then a then a downward strike and an upward strike simultaneously to the wrist of the attacker to either make him/her drop the knife or at least create pain in the wrist. It is followed by a backfist type strike to the face and then a side kick to the throat. I find it very effective and not all that difficult to perform. As for a slashing attack with a knife, we learn to take 45 degree angles to escape the slash. At the correct moment, you step into the attacker and block the arm and strike to the groin at the same time. Then you wrap the attacker's arm and neck, pull him/her into your body and turn to face the opposite direction to throw them. Maintaining the arm wrap, you strike to the throat/collarbone twice, and then explode upward, snapping the arm, and come down with a final strike to the throat/collarbone. This one is a little more complicated, but practice makes perfect. I think I would prefer either of these to the two in the videos, but every situation is different and each person has their preference.