I think I saw that video once. At around 6:50, he said that you want to bring the bar up until your knees are almost straight. That's great if you have a lifter with a long torso and proportionately short legs. Kono seems to have that build. The lifter demonstrating the lifts has that type of build, which is rare because most women have proportionately long legs. I also have that build. When I finish my first pull, I don't need to completely straighten my legs to get the bar past my knees and still stay over the bar. My long torso allows me to do that while still have some bend in my knees. Basically, when the bar gets past my knees, I'm pretty already in the power position. Kono has a problem with a very exaggerated double knee bend as his lifter demonstrates. I agree. You want to use your glutes and hams as well as your quads during the second pull. You don't want to be in a position where your torso is vertical and your knees are bent so that you're only using your quads. I don't have that problem. My double knee bend is very subtle, but it's still there. I suspect many lifters with my body type will also have a subtle double knee bend.
Now, take a tall kid who is all leg, or even a not so tall kid who has proportionately long legs (one of my coaches was like this - although he was only 5'3", he had to do some funky things to get the bar past his knees) and it's a different story. A lifter with those proportions will need to get into a stiff-legged deadlift position to get the bar past the knees. Sure, you can clean and snatch from a stiff-legged deadlift position but you won't get much power.
The bottom line is that you want some bend in the knees during the second pull. The second pull has been compared to a maximum vertical jump and this is accurate. When you try to jump as high as you can, you'll bend at the waist, knees, and ankles - that's the same triple extension used in weightlifting. Try jumping by just bending forward at the waist with bending your knees or ankles. You might jump a little just from the upward momentum of your upper body, but you won't jump that high.