Oh, I built a homemade version of this axe. Mine was a slightly different design, but basically it used kinetic
energy to help split wood.
There are different versions of them. One has it so as the axe comes down, it help drive out wedges that help split the wood farther apart. An off-set axe design is designed so that as it comes down, the axe twists in the cut wedging the wood apart further. My axe design was on a spring, a hinge and also off-set, so that it flipped the split wood out to one side. All the spring did was return the axe head from the flipped out position, back to vertical for the next strike.
It worked pretty good, just kind of too good. it sent the split pieces flying across the
lawn, making for a lot of walking to pick them up.