Oh such little faith, LOL.
I have a set and they really do work. Using them takes a normal pushup and makes it so that the motion is more natural and less stressing on your joints. But, not only that, it also places the effort of the motion on all the correct muscle groups, giving you a better overall effect.
Initially I could only do 10 to 12 of them at a time when I first bought them. Now, with my feet up on a regular sized chair, I can do 30 to 40 of them.
I would recommend getting them. Not only that, but a former Navy SEAL invented them, so I'm sort of partial to that sort of thing. :P