I used to believe that the original workout was the only one worth doing. However, I recently started making month-long rotations like the following:
Monday: Cardio Emphasis Video
Tuesday: Upper Body Circuit
Wednesday: Lower Body Circuit
Thursday: Cardio Emphasis Video
Friday: Upper Body Video
Saturday: Kickboxing
Sunday: Total Body Weight Lifting Video
With the premixes, I can easily fit her new series into this rotation format because I can easily use the appropriate premix for the respective day.
Frequently, the premix is more difficult than the actual workout. For instance, in DrillMax I often find that my heart rate goes down during the weight sections as compared to the cardio sections. However, when I do the Ultra Cardio Blast premix (Drills: 1,1,2,2,3,3,4,4,5,5,6,6), my heart rate stays high and it is difficult, albeit in a different way than the original DM. That workout is still over an hour long, which I like.
Unlike many of the others who have posted here, I use premixes not because they are timesavers, because I do have the time to do a 90 minute workout every day, but because they provide more variety for me to reach my goals.
I hope that helped...