I'm not Kepi, but I also have Cardio and Flex.
The good points: there is no miscounting of sides or reps, which seems to be standard practice with almost every onther Tae Bo workout (including the "Ultimate" workouts, which are reeddited from previous workouts--go figure!). The "Flex" technique is rather interesting: after you do a certain number of reps of a move, you do a "flex" set: 7 reps, then hold an isometric contraction on 8 for 8 reps.
The bad: the intensity is quite a bit lower than the regular Tae Bo workouts. "Cardio" was rather unspectacular. In one of the workouts (Flex?) you do about 25 minutes of the workout, then there is a cool-down/demo segment that takes around 8 minutes, then you do more drills. Huh? Billy, while counting better and being more aware of balance, seems rather repressed in this workout. His usual spark just isn't there.
I have only done these once each, and will do them again because I have them, but if I had previewed them before buying, I woulnd't have bought them.