Book of Glyph Mastery - What's the Deal?

Although I was only in the JMTC meeting for a short time last night, there was a bit of a debate on how exactly Books of Glyph Mastery really work....do they teach you old school recipies? Do they teach only "un-teachables"? Is unteachables even a word? When leveling my scribe, I was popping the Book of Glyph Mastery like they were going outta style. Having not completed all of the "minor"