Clip 1: Coach Yu explains that the catch, specifically the reestablishing of the feet, needs to be just as active as the rest of the lift. You can see in the first clean I just floated and let my feet land and so my catch timing with the bar was soft and weak. The second clean I actively slammed my heels back down right as my elbows turn over. Much stronger and quick.
Clips 2 & 3: You can see the difference between a weak extension vs a full body extension. In the second clean my upper body extends hard along with my lower body. This also contributes to my stronger, active catch.
Picture 1: Glutes and upper back, no extension.
Picture 2: Full extension. Don't confuse a full extension with leaning back. Leaning back involves bending at the lower back, whereas full extension results from driving the chest and shoulders up. The body arch is not as extreme.
Sidenotes: Yes it is perfectly fine to clean with straps. Just don't be an idiot.