> Many e-books vendors frequently reduce their value by limiting access to a specific app/reader, or limit how useful the functionality you describe can be Yup

> Many e-books vendors frequently reduce their value by limiting access to a specific app/reader, or limit how useful the functionality you describe can be Yup, this is why I'm a fan of the likebook/boox type e readers. They all run stripped down versions of Android and many of them have SD card slots too. I use the likebook Mars (~$200) as my daily reader only (bigger ones are nice if your budget allows) and it is so much nicer than the Kindles imo. Default reader can handle all formats, you can dump your own fonts and dictionaries on it, and you can run the Kindle, kobo, libby, etc apps if you want to (since you can use Google play). Ofc being a cheap Chinese e reader it isn't exactly something that can run real apps at more than a couple fps but it's great for static content like books.