A shoe to create a problem not correct one. If you look at the picture posted on their website of the woman running gravitydefyer.com/
you will note she is running with absolutely faulty running mechanics. You never want to land on your heel with you knee locked and your center of mass behind your foot strike. Doing that will cause major injuries over time. Adding the springs to the heel of the shoe do nothing to correct that problem or mitigate it since landing on with a heel first foot strike is faulty body mechanics.