I have started to listen to book summaries via the Headway app. After a month or so here is a list of the pros and cons.
The summaries are only 15 minutes long so you know that you can fit one or two book summaries in a short morning walk (which is also something I decided to do, to limit the risks of working remotely)
You get to know quite quickly if a book is worth it or not. Some books, when summarized to their main points, feel absolutely trivial. For example "A Spy's Guide to Thinking" gives you a "brilliant" method: collect data, analyze it, decide, and act. This is not the revelation I was hoping for
You can "read" numerous books on the same topic, which often serves to reinforce a particular point for you. For instance, there are several books centred around the idea that focusing intensely on one thing at a time can be advantageous: Focus, The One Thing, Essentialism, etc. Similarly, there are many books about habits: Atomic Habits, Eat That Frog, The Power of Habit, and so on.
The voice reading the books can be a bit monochord
The worth of certain books lies in the anecdotes they share. Skipping these to reach the main points robs you of the potent emotions that an anecdote can evoke.
Some books are just so dense that trying to summarize them is ridiculous. For example the summary of Behave, by Robert Sapolsky, which I have otherwise read entirely, is laughable. Not only Robert Sapolsky includes tons of insightful study results in his book but the way he confronts them is possibly the most important message of the book. This is what it means to use science to understand the world (If you want to get a glimpse of the process, go and watch his lectures on "Introduction to human behaviour")
The quality of the summaries can vary. I wish I could recall the precise example, but one summary stated, "Did you know that only 10,000 hydrogen cars are produced each year?" I'm fabricating this, as it was some not-so-interesting fact. However, what was truly intriguing was the reason behind it: "There isn't enough palladium, and there never will be" (again, making this up).
I tried to "read" a book like 1984. I know, I should have read it entirely before and I'm not proud. Reading the summary is not worth it. It's a bit like reading the plot of a movie on Wikipedia
Even summaries feel like they could be sometimes summarized. Ultralearning spends 90% of the time telling how great it is to be an ultra-learner, how some people are ultra-learners, oh and wait, did you know that there are benefits to ultra-learning? And then there is one chapter with some real tips on how to do it
In summary (ha! 😀), I believe that book summaries can serve as a helpful method for navigating the landscape of essays. However, they will never replace the time spent reading entire books, nor will they substitute the time dedicated to studying them thoroughly (taking notes, formulating your own questions or summaries, delving deeper into certain sections, etc.).