The Diana Walstad el natural tank method relies on naturally produced CO2 from organic decomposition of matter in the substrate. But, of course, that method also requires that the light be limited to low intensity, so the plants growth rate will not be high enough to require more than minimal CO2. Reading the "review" of this product seems like it is just a misapplication of the Walstad method, and putting the pellets, which look like ordinary hydroton pellets, in the filter doesn't seem reasonable. Also, that "review" raves about how stable the nitrogen cycle is with the pellets - all nitrogen cycles, meaning the colonies of beneficial bacteria on all wet surfaces, are pretty stable. You can do as big a water change as you want, since the bacteria live on surfaces, not in the water.
Even the description of the enormous surface area of the pellets should be taken in context - all baked clay products have that huge surface area, which helps them to have a high CEC. Those pellets are almost certainly a generic hydroton-like product, which is very inexpensive.