Excellent supplement to the Legend Core Rulebook. Due to space and cost considerations, Mongoose had to leave the Spirit Magic section out of the core rulebook. However with the release of Legend they kindly packaged the section, incorporating the "Shamanism for Fun and Prophets" article from Signs & Portents Magazine 89, and released it under the OGL.
If you check the Legend Core Rulebook, you'll find that it still mentions "four kinds of magic." Spirit Magic is the fourth kind, making this book essential to Legend, particularly if you want to give your shaman characters spirit magic with real bite to it, a match for any of the other magic types - Common Magic, Divine Magic and Sorcery.
I do more than recommend it - you will need it.