I've not seen that before. The site says that it has carbon, volcanic rock and silicate and my guess is that they are what makes it work. If you put carbon in a flow thru type container in the pond, it is bound to help with tanins and will work even better with water flowing thru it. I imagine the volcanic rock provides a place for bacteria to grow, further helping with water clearing.
The prices are higher than just going and buying carbon, but not so high as to be prohibitive. If you decide to try it, let us know how it works.