So, I picked this up a little while back, and my GM asked for a look-see when I told him about it. A few weeks later, he started freestyle worldbuilding a megadungeon that produced its own monsters because of a Major Cosmic Evil(tm) that had been sealed within, and a city around it whose economy was largely based on... the use of monster parts harvested within!
We accidentally bullied him into running a campaign there, and I'm going to be in charge of the loot tables when it starts. Session Zero should be in a few weeks, when the college kids among us are done with finals. The three of us have our characters done - Aberrant Mind Sorcerer, Arcane Trickster Rogue, and Battle Master Fighter, all starting at level one with the Heroic statblock - and we're extremely excited to be using the book and playing this game.
I dunno if I'll be able to edit this with updates on the campaign, but I'm excited! To review the actual product for everyone wanting concrete details and not simple joy - the tables are simple and easy to follow with a dedicated fluff section detailing what any given part is and what it's used for, and humanoid creatures deliberately have a short parts table supplemented with a more traditional loot table, in case your players hack up bandits instead of leaving the corpses in peace. The rules for appraisal and actual harvesting are simple and intuitive, with parts being assigned a DC to reach per creature type (say, parts at DC 10, 15, and 20 for any given harvesting roll) rather than having to aim for specific parts in different checks, each with an attached value on sale and listing any potential uses. Not all items are unique to this book - several are instead found in official materials, with only rules for how to craft them; I consider this to be a good thing, because let's be honest, your players are absolutely going to ask to craft basic arrows at some point, if they're the sorts looking to craft at all.
Altogether, this book is simple and intuitive to use, doesn't overstay its welcome, and does exactly what it tells you it will. I'm planning to get the follow-ups at some point in the future if we ever start eyeing creatures outside the MM.
[5 of 5 Stars!]