From the description on their site, it looks like this stuff is a mixture of activated "super" carbon and ion exchange resin. Both are used for purifying water, but in differnet ways. The IX resin traps ions of a certain polarity and relative electronegativity while releasing similar ions with a weaker electronegativity. The carbon is useful for removing organic compounds and some trace elements.
With that being said, I would not use this for a planted tank. In a planted tank, you want as close to "natural" water as possible. Pure water might work well for a SW-type tank, but not with a planted tank. Even a FOWLR tank needs some nutrients in the water, but nothing close to what is needed for a planted tank. The description of the product isn't very clear on what would happen in a planted tank, but I'd err on the cautious side.
You might be able to use it as a sort of pre-filter on your top-off or refill water. That is assuming that you add ferts back to the tank regularly.
In the end, I think you'd be better off without it.