Unlike an ordinary mallet, this one contains a loose weight of buckshot, which flies forward inside the head at the moment of impact to counteract recoil. The mallet head strikes the object and just stops, dead, that's it!
None of the energy is dispersed as bounce and vibration, so it all goes straight into the workpiece; and you don't have to waste any energy bringing the reactionary forces under control.
Much more control, much less effort and no damage.
You'll wonder how you managed without one.