Greetings,
Actually yes, I have seen a similar one in action.
The owner must have used it quite a bit as he was pretty good and quick with it.
Granted he was not as fast as anyone who had spent over an hour or two on a real hoe but he built his own and didn't have the 6 to 8 grand invested in a regular hoe - it WAS as fast as a some of the "compact toys" with short booms doing straight trenching about 2 feet deep.....but then he WASN'T in the clay where I live!
Most private people (not commercial users) with a hoe only use it a little - and if you figure the cost vs hours used, it comes out to hundreds if not thousands per hour.....until you use it a lot!
If you look around at the skidsteer bunch, they have something similar but use a regular shapped bucket but the skidsteer version is much quicker due to the manueverability of the machines it's attached to.