Oh, it is a great series, I would definately get it, and I do find it challenging. You can do them on a daily basis (6 days in a row with Sunday off), or seperate. I find myself reaching for them alot now when I have just finished a weight workout and want a little cardio. Also, if I know I am going to have a tight week, I will do the whole series. You will really enjoy them. Alicia