I have done a round of Insanity. Awesome program. Extremely tough and I'm not just saying that. Even though it doesn't use any weights, I got my leanest and most toned from that workout. If you're looking for more cardio, I would recommend Turbo Fire as well. I used that in combination with STS and got amazing results. It's probably the most enjoyable workout I've done. Tons of fun, tons of energy and it is definitely challenging.