This is a decent contribution to the Sex Pistols/Sid Vicious library which isn't afraid to challenge conventional accounts of the story.
The fact that the author lived with the subject's mother for a time will obviously mean he has a certain angle. But that shouldn't put you off - in fact it means he gets some proper insights and quotes.
It's interesting to have some details of Sid's short but eventful life and career that weren't widely available at the time. His childhood, including a brief pre-school period spent in Ibiza, apparently impressing the locals with his knowledge of Spanish swear words, is dealt with at length, and his musical tastes before the Sex Pistols entered the public domain in 1976, also provide surprises: was he really a Presley and Abba fan?
We're already aware of the politics behind his appointment to the Sex Pistols as bassist after the sacking of Glen Matlock, despite him being less than adept on the instrument. Thanks to the tabloids, we know enough about the mutually destructive relationship with Nancy Spungen that led to his death. Parker does a good job at presenting an alternative view: his account of Spungen's murder is well-argued and perfectly plausible, disputing the papers' simplistic claim that Sid stabbed his girlfriend to death as part of an eventually successful suicide pact.
Where the book is weaker is in the handling of the various versions of Sid Vicious that the author has been given. Clearly different witnesses will give different perspectives, and we know about the man's "mercurial" character, obviously influenced by drugs. But we don't get a clear picture: was he a weakling or a bully, was his stage name honest or ironic, was he a halfwit (the consensual view both in his lifetime and post mortem) or a budding intellectual?
The relationship with John Lydon is somewhat oversimplified. Lydon, who is not credited as a source for the book, is painted as a former best mate who abandons and then ridicules his former friend and colleague. His own post- Sex Pistols career in Public Image Limited is rather diminished - strange seeing that PiL had a longevity and musical sophistication not allowed the Pistols or their ad hoc offshoots like The Professionals and The Vicious White Kids.
Finally, some of the spelling mistakes of people's names make for an unnecessary irritation. "Debby" Harry, Eddie "Cochrane" and "Vivienne" Goldman, among others, unless they've changed their names without telling anybody, might be slightly upset by this carelessness.
It's up to you whether you want to let this put you off. Maybe it's fitting, given the nature of punk rock?