Their claim that 5 ppm FC is a problem may not have any understanding of the FC/CYA relationship because it should be the active chlorine level that is relevant towards the degradation of the biological material. 5 ppm FC by itself means nothing. It has to be understood in the context of the CYA level. So I would not assume that a higher FC, when the CYA is proportionately higher, will be any problem for this product.
I am either miss-understanding your statement or I have missed the boat in my understanding of the FC/CYA chart provided here. My understanding is that FC is FC no matter how much CYA is in the water. HOWEVER the more CYA that is in the water the more FC is required in order to be effective. Therefore if they require 5ppm FC or less is doesn't matter how much CYA is in the pool because 5ppm FC is 5ppm FC regardless. Please let me know what i am missing.
Just my 2 cents on this product--- I am very reserved when it comes to optimism. For our company I would put it in the revolutionary dept if this product holds true.