I was able to put on 12lbs in the 6 weeks, but that's honestly not even what is good about the program. The program is a hard lesson in what it means to actually work. Those 20 reps (if done properly) will basically kill your soul, and you'll be doing that 3 times a week. That means it will be up to YOU to commit and put in the effort each workout, despite the fact that everything in your mind and body will be screaming at you to stop. Most folks simply don't have the discipline and willpower to pull it off, but doing it will really pay off for any training.
Additionally, you will learn how to be obsessed with progress. As much as you might dread every workout, if you ever miss all 20 reps (failing at rep 18 or 19) you will be torturing yourself mentally until the next workout when you finally have a chance to redeem yourself. You will live, breathe, eat and sleep 20 rep squats.
It's also a valuable lesson in recovery. Learning how to eat and rest enough to recover from workouts.
And also a good way to understand how rest pausing works.
As for your other question, are you looking to build or peak your squat?