Aside from the merits of Pineal Guardian, is their thesis correct that pineal gland calcification driven by fluoride accumulation causes lowered melatonin production which impairs brain function?

Not only is this correct, it is understating the central importance of pineal gland function in maintaining a number of important regulatory functions by the brain in its influence on the body as a whole, much still unknown to science. So this deserves a place among the top tier of nutraceuticals for maintaining and restoring brain health and function.