Hi Patrick.
I can't recall the exact percentages of protein content of FBS at this moment but it is generally much lower than BH of FDBW . And proteins are most important when it comes to growing discus .
They are claimed to be 90 % of water from their total weight and low protein content , so I recommend using them only as a occasional treat to your dicus rather then a main food source.
They are also claimed to be effective for cleaning discus Intestine from other protein heavy feeds .
I've also heard that occasional FBS feeds can keep some gut parasites at check because of their salt content but I'm not sure how true this claimings really are .