This was very good with a lot of interesting information and anecdotes. I've read about a lot of these people before, but I'm a sucker for year-by-year books and books about the 1920s, so it was perfect for me. I occasionally lost track of who was who (I fully admit I'm not great with non-English names), so sometimes a person by person approach may have better, but I love books that progress through time, so ultimately I really enjoyed it.
I haven't read any Tommy and Tuppence before (that I recall anyhow), so didn't know what to expect. I know they age over their books, but didn't realize they were so young at the beginning!
This wasn't my favorite Christie, but in the end I liked it. I'm not really a fan of spy/espionage stuff, so I think that was part of my dislike. I did like all the various identity stuff and the relationship between Tommy and Tuppence.