Reading the summary gets you through the quiz. Reading the book gets you through the conversation after.

A summary hands you conclusions without the thinking that produced them, which is plenty for answering questions that already have answers and nothing beyond that. The moment somebody asks what you made of it, or pushes back, there is no material underneath to work with. Depth only comes from time spent inside the thing, and there is no compressed version of that.

Read the real thing when it matters to you, and use summaries for what they are good at, which is coverage under pressure. Know which situation you are in before you choose.