The Fama Fraternitatis RC and "Book M"

I came across something in my reading today that made me think. I was reading this page: http://www.sirbacon.org/mcompeer2.htm and I noticed a statement about the story of the first Brothers of the Rosicrucians as described in the allegorical story in the Fama Fraternitatis RC (Fame Fraternity, or a Discovery of The Most Noble Order of The Rosy Cross (hereafter referred to as The Fama)).

According to The Fama, the first Brothers of the Rose Cross wrote a book that is only referred to as "Book M" in The Fama. This made me wonder, is "Book M" the "Monster," or the "Monster with four legs and two voices." In other words, is it the First Folio of Shakespeare, which I believe was referred to as the "Monster" with four legs and two voices?