i think this is something only SA cichlid keepers would use.
from what i've read, it appears that the truly soft water cichlids like some apistos, wild discus, angels and maybe true parrots would require these extracts.
most of the commercially bred fish should have more or less acclimated to our current water conditions.
i've personally never used it before so i can't comment.
i believe tetra has blackwater extract.
I now a lot of geos originate in many rivers near the amazon but not sure if they are in actual blackwater conditions or if it would help increase spawning.
i used it but it kinda sucked, never really helped anything, just made it more difficult to see the fish. If I recall it didn't even break my buffer in my tapwater, so that sucked.
It was with discus as well, i used peat moss, and it was very tea colored. I ended up just forgetting the idea and keepin the pH constant instead of accidentally swaying it becasue of my buffer in my tap water.