Is it good for toning?
Yes, but I guess it depends on what you are used to. I tend to build muscle pretty easily so I like to stay away from squats,etc. because then my legs get a little too muscular for my taste. With Fluidity, I have a *leaner* looking muscle. I have doing the workouts really regularly this past month and have a noticeable difference in my seat, thighs and waist. My calves have also gotten a nice, slender curve to them(not a *hard* muscular look.)
Is it challenging?
Yes, but, again, it depends on what your used to. You are working within a very limited range of motion and the moves are very subtle. Form and focus are everything. If you don't really follow Michelle's instructions on form or really pay attention to staying in correct form and concentrating on each movement you can make these workouts really easy.
Obviously, the intermediate and advanced are tougher than the Beginner workout but the beginner still has some tough moves. There is a modifier in every workout as well as an *advanced* modifier. Michelle always says that she is intermediate. So, you can do the beginner workout and try to follow the advanced modifier if you find it too easy.
As I said I have been doing these workouts consistently for a month and there are still quite a few exercises that I can't complete the set on yet because my legs are just burning way too much
I don't want to neglect to mention that there is upper body work and ab work in each video. Some may find that upper body work is not that challenging. I like the Intermediate/Advanced arm work with the bands, but I don't usually lift heavy upper body weights.