I agree it had limited research- to think Isadora with Vanessa Redgrave is by Ken is a reasonable mistake, unless you had actually seen Ken's film Isadora Duncan. Writing about films without having seen them is just bluffing. As you say lots of other errors, and I didn't learn anything new, but I did find it a good quick read, maybe it was a good reason to be nostalgic.
I did have the very strange experience of reading the book in the tube (subway), and suddenly coming across a paragraph where I am mentioned and quoted. You instantly want to tell all the other passengers (fortunately I didn't).
The BFI (British Film Institute) have done a lot of good work on Ken, both in issuing his work and showing his films.
Iain