I've used it for a season back in my teens. I was impressed back then. I've since come to see that the energy translated to expansion force via the side levers, only marginally eclipses that of modern maul heads such as the Helko Tomahawk or Fiskars Super splitting axe. But is offset by it's larger edge surface and geometry. All in all, I'm sure a side by side comparison would reveal that, while the Chopper 1's heart is in the right place, it's design and function are not as efficient as one might initially suppose.
If one wanted to get technical, it would not be too difficult to measure head speed for comparison at moment of impact, between it and other axes, on wood cut from the same log with sufficient composite similarity to warrant such a test. Most would be able to analyze well enough by feel, I imagine, to preclude the need.
Of course, this is not to say that there is not appreciable room for greater efficiency in modern splitting axe head design.
TS