Slim Series workouts are very different from Cathe's workouts: high rep, low or no weight resistance. Most of the workouts are very similar to each other: squats, lunges, light weight upper body work. Debbie Siebers, the instructor, has a bad sense of rythym (she's off the beat of the music quite often. There is a "music off" option that I use, and play my own music, following the beat of the music rather than what Debbie is doing).
I did the Slim Rotation for about 2 weeks, but I missed heavy upper body work so slipped in S&H chest/back during week two.
The rotation seems to work in the short run (my waist especially looked trimmer after the two weeks), but I don't know if one can maintain the results very easily. I didn't once I went back to other workouts.
Debbie is also not very good with form, and includes some risky moves, like FAST deadlifts and upright rows with elbows very high, and double-time moves I found to be not so good on the joints. If you have a good knowledge of safe form, that shouldn't be a problem.