Tells the story of the early years of the Mothers, not from Frank's perspective, but from that of many of his early band mates. There's perhaps not a ton of new information, although there are some fun little stories and interesting angles on events in Mothers/Zappa history that differ from Frank's.
One example that stands out is a story from the legendary "Pigs & Repugnants" residency at the Garrick in NY. Frank tells a story of how one night he called some Marines on-stage and had them destroy a toy baby. Frank always used the story as an example of how f'd up American military culture was: the Marines had been turned into bloodthirsty animals who got off on recreating the violent atrocities they committed in Vietnam.
As it is told here, however, the Marines did not want to go to Vietnam, and their performance was an act of protest: this is what they are making us do to babies in Vietnam, and we don't want to do it.
In this case, I think that the more sympathetic version is probably the truer one. I think Frank revised the story in his memory to match his general cynicism -- and he's not wrong when it comes to his cynicism. But in this case, I think he turned the story into an example to support his disdain for American militarism.
Back to the book: the biggest insight is perhaps the importance of the other Mothers to Frank's early musical output. Frank liked to downplay the contributions of others -- and to some extent, there's a little bit of boasting and exaggeration on the part of some of the band members here -- but Frank would not have developed the Zappa sound without the contributions of the original band members, and more because of the amateur quality of some of them as musicians, rather than despite it. I still prefer his 1970s fusion-esque stuff a bit to the early Mothers, but there's no denying that the early Mothers were a band apart, and no matter how awesome the later musicians in Frank's bands were, I don't think they every matched the chaotic creativity (with all its rough edges) of the first few years. I know that if I could ever have been in one of Frank's bands, these years definitely would have been the most fun.