I have these DVDS, I would say that I like the "high and tight" DVD the best. The ab work is pretty good, the cardio is okay but dancy, since your SIL does zumba she may enjoy the cardio. If i remember correctly each DVD is about 30" so I used them as "add ons" after another w/o.
Leonardo's personality in this series is very likable which I find important, I hate buying a DVD to find out I can't stand listening to the instructor. I recently bought a Jillian Michael DVD and although a very good DVD I do not like her personality in it so I never do it. I would do this DVD much more if I could "mute" it.
I can honestly say that I rarely use these DVDs anymore as Cathe's turbo barre and lower body blast are so much better!!!.
Hope this helps,
Katie