The supplement does exactly what it says on the thin - it describes (through random tables) a snake cult, with multiple possible members, tenets, poisons and taboos. It looks - and reads - like a black metal album, with lots of blood, gore, NSFW art and appropriately grotesque ideas.
Like most of Rafael's stuff, this supplement pulls no punches. It is weird, creative and extremely useful if your game features any kind of evil cult or religion, not only ophidic ones (also, any adventures featuring snake-people of any kind might benefit). You get things that you can use to create adventures, dungeons, factions, NPCs and monsters; motives to fight the cult, make deals with them, loot their temples or even join the group. Also half a dozen tongue-twister if you ever need them!
The ideas described in there are compatible with "regular" fantasy RPGs, but very different from most "vanilla" cults you'll find in most of them - even the horror-themed ones. Less "sacrificing innocent people to serpent god" and more "In a public place, you must [shove] a serpent into the body [mouth, wound, etc] of a powerful foe with many allies [...] so that all know the cost of opposition".
It packs a lot of content in its 32 pages, so much that I almost wish all RPGs were written that way. Its fun and easy to read.
I have both the PDF (PWYW) and the print version from Lulu, and I recommend both (check the PDF first; as a 32 page paperback, the print version is not impressive to look at but worth the price).
If any of this interests you, this book is, undoubtedly, a good use of both your time and your money.