Martin Brungard posted this on his Facebook account. I hope he doesn't mind me reposting it here, but I wanted to have it archived where we could all find it.
"Here is a comment from noted brewing water expert, AJ DeLange about the conversation he had with the chemist from Five Star Chemicals regarding their 5.2 Stabilizer product.
"Tipped a few last night with the chemist who designed this product and was able to confirm that it is indeed a mix of phosphates (mono and di basic) that accounts for the presence of the malt phosphate. This is something I have long suspected and am pleased to have finally confirmed.
Good manners prevented me from pressing him on its efficacy and suitability relative to the statement on the label but his comments on it were basically that most brewers shouldn't use it/need it and that it was put together for a particular brewery that had variable source water and no desire to make any effort to track that variability."
Please spread the word that the 5.2 product is not needed or desirable for brewing."