I’ve opened some. It’s genius, it’s like a giant webpage with lots of information, but without all the ads, cookie banners, etc. Unfortunately the ones I have don’t seem to support any way to quickly search in the text. Though they’ve also thought about that, rather than implementing search these books tend to have a big overview at the start with all the separate chapters and sometimes a search index of commonly searched words at the end. Quite genius for what’s effectively just a neat monitor stand