This is a good basic introduction to the history of the development of equal temperament, with a focus on the problems this creates for performing music, especially works created before the acceptance of equal temperament. However, for many readers, the lack of audio supplements will render much of the details of various tuning systems meaningless. For many casual listeners the distinctions Duffin discusses may just seem esoteric.

While Duffin covers trends in the modern performances of Renaissance & early classical music that include a return to non-equal tempered scales, I'm disappointed that there's no discussion of the various 20th and 21st century composers who have used just intonation tunings in their music. There are many. Some created new acoustic instruments to play music using unusual intervals and tunings. These include the pioneering Harry Partch, as well as Ellen Fullman, Kraig Grady, among others. Others made compositions for traditional instruments tuned in just intonation. These include Lou Harrison, Ben Johnston, Pauline Oliveros, James Tenney, again, among others. Still others use electronic instruments and/or software to make create music in just intonation.

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Well written book, technically not a treatise, not written in a scholarly manner but still informative. RWD makes a good argument for non equal temperament.