I came across a copy of this at Goodwill and was sort of intrigued by the concept. When I sat down to read it I used it as an opportunity to listen through all the symphonies listed in here.
I was surprised to realize that I knew most of them, but simply hadn't associated a composer with them. The commentary that breaks down each symphony is fairly basic and I found it accessible and helpful since I have no formal musical training (piano lessons when I was 10 I don't think count). It certainly opened up some parts of the music for me. I also liked how he had put words to most of the themes or tunes that can be found in the symphonies as a way to identify them if you hear them out in the world and are trying to identify that piece of music. It's a clever way to keep them in your memory.
I discovered through listening to all the symphonies here that I like the earlier composers symphonies more than the later ones, Dvorak's New World Symphony excepted. I am also not a fan of Beethoven's symphonies. I think this would make a great introduction to Western European classical music for kids or parents looking to dive in, but unfortunately it's not in print anymore.
I found the conceit of attributing silly phrases to the symphonic theme rather annoying. 'Let's hurry with Haydn to wind the clock' might make it easier to remember the theme of Haydn's Symphony #101 (The Clock), but ultimately destroys the pleasure of listening. Giving words to the wordless impresses ideas that were not necessarily intended by the artist. But looking at the title, I guess Spaeth's goal was simply to provide a mnemonic devise for identifying the piece. Not my cup of tea.