Both are great books.
If you/they normally read fiction and don't will reject anything overtly Bitcoin, The Mandibles is a great subtle approach.
If the group normally read non-fiction - Broken Money is great. Same with The Bitcoin Standard.
Tangential - but if you're ever looking for Bitcoin Fiction - give us a shot.
Mysteries of the Bitcoin Citadel (Audio Drama)
Bitcoin. Secrets. Betrayal.