This exercise is right up there with Plyometrics. The only major difference is; Plyo was intense cardio, this is some intense muscle building. If I had to place this exercise in the gambit of others, I'd put it as number-2 most difficult so far. That being said, I'm having a hard time remembering Chest&Back (my previously rated #2).
Tony comments at the end "If you did this right, you did over 120 pullups." Okay, I didn't actually achieve 120 pullups, but I added up my sheet and I was able to do over 100. Not bad. I really liked the switch-grip chinups. I was really able to push myself hard to get in the mid-teens. I attempted using a chair a couple times - I didn't enjoy it. I think I'd rather struggle on my last few than use a chair. We'll see if that changes later. My avg pullup was in the 12-13 range (up +2 from chest&back).
But the pull-ups were NOT the hardest part! The sets of 2-3 wall squats + deep lunges were brutal. The sneaky-lunges and the 80-20's were both very challenging. Infact nearly all the exercises really tested my abilities. I often found myself putting my hands on my knees to get up. I'll try to reduce that next round.