I am very late to the Caroline party, having just discovered her late last year. I have completed:
Iron
Tempo
Fuel
Beastmode (currently in my second week).
I have to say, I love all of them so far.
Fuel was more metabolic than Iron, but I thought Iron left lots of room/energy for my own cardio. Fuel kicked up my cardio capacity a notch or two for sure.
Tempo is one week, and Beastmode is 2 weeks, however I can see the value in repeating them immediately to gauge progress.
I think Epic III may be next for me depending on when STS 2.0 is released. I am looking forward to see how Cathe schedules them for use in rotations.
With Caroline, I am lifting heavier than ever, and feeling efficient in my workouts.