GOOOOOOOD MORNING LIVEFITTERS!!!!
Funny you ask this question. I was so used to doing circuits back when I was at a gym, that I did it the way for my entire "Round 1" (with supersets, I just wouldn't rest the minute in between).
It only occurred to me at the end of the 12 weeks that Jamie intended it to be 3x each exercise (minute rests between sets) before moving on to the next exercise set. Boy, did I feel silly. So this round I am doing it the "correct" way.
Sometimes I think its harder, but it doesn't feel significantly harder. Mentally its actually EASIER-- like when I get to a dreaded exercise, I get to get it over with right away (instead of dreading it over and over again each time I'd repeat the circuit). Plus now, I'm not changing weights over and over.