Hi,
Well that data only indicates that the clay might be hard baked. If someone adds fertilizer to a clay product then they have to say what fertilizer is added to the clay. For example, in the case of enriched products such as ADA Amazonia, the clay is baked with peat, NPK and micronutrients on the surface, but the temperature that it is baked at isn't very high, so the clay remains soft and can cloud the water. At higher temperatures the clay begins to harden so that the clouding is reduced.
Clay has a property called Cation Exchange Capacity (CEC) in which the positively charged nutrient ions in the water are electrostatically attracted to the surface of the clay. So, for example a cation such as ammonium (NH4+) or Potassium (K+) can be passed on from the water which surrounds the clay particle. Root hairs that make contact with the clay surface can electrically sense the presence of the nutrient and configure the root hairs with a negative charge to pull the positively charged particle away from the clay surface and into the root.
It is a very broad statement to say that it "provides aquarium plants over a very long period of time with all the necessary nutrients." What are they considering to be necessary? Trace metals only? That means nothing, because the clay will continue to exhibit the CEC properties for a long time. In fact, that's how it affects the pH, by attracting those ions in the water which affect the alkalinity of the water, such as Carbonate and Bicarbonate (which every clay product does to a greater or lesser extent) so there is nothing extraordinary about this property that is not also in many other clay products such as cat litter, molar clay or even Bonzai soil such as Akadama. Read the Akadama sticky at the top of this forum section. People are constantly being fooled by claims of revolutionary product performance when in truth, the ability of the product is based on the simple property of rocks dug out of the ground. You can find molar clay in any garden center which do exactly the same thing as Ferti-Soil for much cheaper.
You should always be skeptical when the product does not list specific nutrient components and when they issue broad general statement such as that quoted above. There is nothing special about the structure which gives the plant roots any special advantage.
If I were you, unless the local water supply was high in nutrients, I would not depend on the nutrient capability of this product alone, especially if you intend to inject CO2. Email them and ask them what specific nutrients are added to the top coat. If they provide the data, and if you are satisfied with that then fine, but do not fall prey to marketing hyperbola.
Cheers,