I am really liking this method, and I don't see myself switching anytime soon. I'm happy with my body, I feel great, strong and full of energy all the time, and that in exchange of 5 hours of exercise a week is totally worth it.
So after becoming very acquainted with the Mat Workout (which I've been doing for over 5 months now and heartily recommend), I decided to order the Perfect Design, which by the way is about 16x as expensive for some reason.
I've only been doing it for a week, so I cannot really say long term effects, but I can tell you that it is much more challenging, it works your body together all the time the entire time, and is really hard on the buttocks. It keeps you a lot more active as a whole, and you sweat, and you get tired.
I've been alternating it with the Mat Workout, because the Perfect Designs doesn't have a section for arms with weights, and that is very necessary for me. I think they make a perfect pairing if you alternate them, because the Mat is a very clear succession of exercises that work all of your body very neatly, whereas the Perfect Design is a fast, cardiovascular exercise, with emphasis on the buttocks.
Word of warning: Where the Mat was hard on your joints, the Perfect design is even more so. You'll have to be quite strong to begin with to do this without injuries. It is very hard on the knees (which you will need to pad a LOT) and on the wrists, which will support your body during many exercises. Same thing with the abs which will be supporting the spine, that gets a lot of twist here.
And I do want to say something here: I have always felt very strongly that the body needs to be protected during exercise, being very guarded and avoiding for years anything that put pressure on joints, or on the spine. But it's very hard to advance if you avoid all impact on your body, because it kind of needs it. In my experience if you do it step by step and slowly, listening to your body and adjusting accordingly, your strength will be your own protection, within reason.
I love the fact that you have total freedom to stretch whenever you want, and you're moving every part of your body all the time. There's so much going, you have to stay so focused that you're finished before you know it.
As always these are just my thoughts/experiences, feel free to contribute or correct me.