We don't walk how we used to because of shoes. We evolved to walk toe-heel, but now (most of us) walk heel-toe. The human foot has a very complex network of tendons and other things to do exactly what this does: absorb and reflect energy. Shoes cushioned our foot, and things like boots in particular led to landing on our heels instead of our toes. Try walking in bare feet heel first, and then swap it around. I guarantee you will notice the difference.
I've seen a fair bit of research that suggests many common foot and leg ailments can be traces to this form of gait. I know that I walk toe first in very thin-profile running shoes. It looks odd compared to the normal gait, but I've noticed that my feet also have very strong, developed arches, which I rarely see on anyone else. I also run toe first--there is a very appreciable difference in the impact that my knees take. I firmly believe it is a healthier way to move. There's a similar idea reflected in the book "Born to Run" about running with the Tarahumara tribe in (I think) part of Mexico. They are renowned for being able to run for virtually forever, and I believe that this can be attributed to the way they run and their diet.
It looks like this device has a 7% efficiency gain over the heel-toe walk, which doesn't really impress me. They aren't improving on nature--they're catching up to a system that nature had already figured out a long time ago. I really can't stand the human ego contained in statements like "The boots mirror the action of the walker's calf muscle and Achilles tendon, saving energy and showing that there is room for improvement in our already very well-tuned gait".
Now, I admit I could be very wrong about all of this. But my experience, as well as simply examining the structure of the human foot, leads me to think that nature already had it right. Toe-heel walking is much more efficient, less harmful to our feet, knees, and legs, and results in fewer injuries.
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