Great interview! Regarding the pump...I have always downplayed it, though when I last interacted with Stuart McRobert, who I used to write for, he believed a back down set was quite viable (12 reps following a heavy 6 rep set for example). Being better suited to low reps, being fast-twitch muscle fibred, I find them tedious. But recently I have taken another look at them, thanks to a friend of mine who's gaining quite well on Matrix training.
Despite purchasing Dr. Laura's book back in 1993, I always poo-poo'd them as another novelty. So I eventually tried them on bb curls (5 full, 5 top to 1/2 way, 5 1/2 way to bottom, 5 full) and was shocked what it did on my poor bis! Not only after the set, but the remainder of the day my arms were next to useless, the discomfort so distressing I literally felt like ripping my biceps out!! Never have I experienced that in the 3+ decades I've lifted.
I now have a renewed appreciation of their merit, and am enjoying playing around with them, even their base; 21's. The discomfort may be excruiating, but the pump and fullness more than makes up for it. Besides, what hardcore bodybuilder doesn't enjoy the rush and fix of a good pump?
Lifter... no-one trains harder!