From the book's inside cover:
The 50 Fathoms Companion is an official accessory to the original 50 Fathoms setting book.
Within these pages you’ll find expanded descriptions of the settlements of Caribdus, more than fifty new Savage Tales, dozens more magic items, and a variety of new beasts for your character to encounter.
Much of this book is designed for the Game Master, though players will find useful information contained within. Although this is an official supplement, you should take Savage Jack’s advice and only use the bits you want for your game.
Prime your pistols, stow your baggage, and prepare to set sail once more on the seas of Caribdus, for new adventures await those of stout heart.