Three things bother me about this book:
1. The chutzpah of Oxford University Press for pricing it as high as they did.
2. The author's habit of criticizing unnamed straw men to make his point.
3. There's little here that isn't covered more thoroughly and more authoritatively in Farkas Art of French Horn Playing and Reynolds The Horn Handbook.
Like Farkas, Schuller prefers a moderate approach to selecting an instrument and mouthpiece. Unlike Farkas, he's not very specific, except he doesn't like big bore horns, by which I think he means large bell throat.
Both criticize what has come to be known as the big American horn sound as being immoderate, without naming names. Could he be referring to the artist Leonard Bernstein called the finest horn player in the world? Principal horn of the Philadelphia Orchestra at the age of 17, principal horn of the New York Philharmonic for 23 years, on the faculty at Juilliard for 42 years? He doesn't say.
Like Farkas, he describes embouchure and airflow, but came to some different conclusions. For example, Schuller says teeth alignment varies when you are playing ascending (with overbite) or descending (with underbite) lines. Farkas recommended aiming the airstream into the center of the mouthpiece. Schuller aims it at the side (top or bottom) of the cup - where depends on pitch. While this is interesting, I suspect most players don't know exactly where their airstream is directed and today most teachers prefer that students think about the sound they want to produce, rather than the mechanics of teeth alignment, airstream, and diaphragm.
Since Schuller is a respected composer as well as a horn player, the chapter directed to composers and conductors promises to be the most interesting. It's only 13 pages. Much of it you can find in any orchestration text: range, include rests for lip recovery and breaths. He says two biggest faults of composers are overusing horn in low register (takes longer to speak and doesn't project) and misunderstanding the variety of muted and stopped sounds available.
He says a good horn part should be hornistic; it helps to think of a modern horn in terms of harmonic series; admires R. Strauss horn parts. The chapter includes a brief description of wave interference: unison playing of horns in close proximity to each other can cause missed notes, as can directing bells toward nearby timpani.
Fifty pages are devoted to a simple listing of repertoire, without comment.
If you are a fan of Mr. Schuller, you'll probably want this book. If you intend to own every book ever written about the horn, it may be a worthwhile addition. Otherwise, you may want to borrow it from a public library before deciding whether it's worth its high price. 137 pages, paperback.