What is really interesting is that I can put comfortable earplugs in to cut outside sounds off and put the bone conduction earphones on and can still hear my music perfectly. I was in a 20 seater turboprop plane over the weekend and with the earplugs in and music going I could barely hear the engine.
Not that these are not worth the money because they definitely are, but he gives his books away for free online on his own website. https://craphound.com/ is the site.