Oh dang. I kinda really like this idea. My new-to-me TLB came with a 16" bucket on the backhoe. Nice compromise of a size, but frankly a little wide for de-stumping given the low power and lightweight nature of my machine (Kioti CK3510se).
So something really narrow for ripping roots with much more concentrated force would be awesome. But swapping backhoe buckets on a daily basis is pretty much out of the question.
As for the video above, I do sorta wonder if that guy could have gotten the tree down just as fast by simply using his backhoe bucket. That was a little tree, after all.
My thought process for toppling a tree, or getting a stump out would probably be: Use your stock backhoe bucket first, to see how far you can easily get on digging up the rootball. Then slip the ripper on, and go to town. Once you've ripped everything you can find or reach, take it off, and finish the job on regular bucket again.