Sound of the Beast sounds good, too many articles / books about old heavy metal are either quite dismissive of Saxon or omit them altogether so this sounds refreshing!
Haven't read Di'Anno's book, but I do have his DVD The Beast in the East. There's an interview section on there where he claims that Saxon, Tygers etc had nothing to do with creating the NWOBHM ... the NWOBHM was Iron Maiden apparently, and the others were "just rock bands" that jumped on the bandwagon later(!).
He also says how he hates playing Maiden songs (but the DVD performance is full of just that!) and how he is really more into punk and hardcore than anything else (but then contributes 3 new tracks as DVD extras and they are soft melodic rock, Dokken-style).
I think Di'Anno just says the first thing to come into his head when he's being interviewed, in order to provoke a reaction and be controversial. You could certainly not accuse him of being boring, and there's nothing wrong with what he does so long as you take it all with a pinch of salt.
His performance on the DVD is less forgivable though. He shouts his way through far too many songs, making no attempt to sing in tune at all and spends more time trying to get the crowd to sing along than sing himself. It might have been okay actually on the night in a live setting but its not really what you want to watch at home on a DVD!