As I've previously mentioned in an update, this is a book that is really aimed at level 10 Christie fans. It spoils the solutions of many of the books, although sometimes the spoiler is fairly oblique. For someone who is just a casual Christie reader, it wouldn't make much sense or, even, be particularly interesting.
For me, though, it was a really fun book to read - although I confess that I skimmed probably more than I read because, while I enjoyed seeing the notes and learning more about Christie's writing process, there was also a lot here that I already knew. Curran focuses very much on the books, not on Christie's life itself, which makes sense given that the notebooks weren't journals - they were writing notes.
There are a couple of short stories at the end that I haven't yet read, but I've finished the sections about the notebooks. It's definitely a resource that I will return to when I reread books, and it does seem to have a good index at the back. I bought it on kindle, but given the quality of the index, I will likely buy a print copy as well so I can more easily use it a reference.
There is a second book that Curran published from the materials in the notebooks. It's a bit more expensive than this one for kindle, so I'll probably just order it used in print from Abe books at some point.