I guess if you had wild caught discus there would be huge benefits but the discus that most are likely to obtain would be tank bred in plain old treated tap water or HMA water.... so really there isn't any need
Rip-off IMO. Just make your own blackwater tank if you must, with things like peat filtration, almond leaves and alder cones on the substrate, and bog wood, etc.
Seachem Discus Buffer and Discus Trace, are far better additives to use. This will not only help buffer the pH, but also contains the correct trace elements that will improve the health of your Discus.