I haven't used it but generally if it's a lighter colour, it's a watered down version of everything else. Unless you are keeping wild caught fishes or breeding soft water fishes from the Amazon or tropical Asia, you don't need blackwater extracts. If you want to make your own, you can add a couple of dry leaves from a deciduous tree to the tank. As these soak they will release tannins (the brown stuff in tea and blackwater) into the water.
Generally any deciduous tree is fine to use, oaks are a favorite of mine because I had an English oak in my backyard when i was a kid. Avoid using conifers (softwoods like pine trees) and any plants that are known to be toxic.
