The main size of readers now is 6 inches. This is enough to read fiction. On Aliexpress, there are devices for 5 inches. I had such a "baby", I had to turn the pages on it often — it was annoying and prevented me from concentrating on reading. Slightly smaller models with a diagonal of up to 8 inches. They are more expensive, but more convenient. Usually they already have built-in backlight, Wi-Fi and other additional functions. Readers with a diagonal of 9 to 13 inches are usually taken to read technical documentation like ITIL foundation book and literature — when it is important to see a lot of information and illustrations on one screen at once.

Watch here:

ITIL foundation book

https://rabota.dev/threads/%D0%92%D1%81%D0%B5%D0%B3%D0%B4%D0%B0-%D0%BB%D0%B8-%D0%BD%D1%83%D0%B6%D0%B5%D0%BD-%D0%93%D0%9E%D0%A1%D0%A2-%D0%BF%D1%80%D0%B8-%D1%80%D0%B0%D0%B7%D1%80%D0%B0%D0%B1%D0%BE%D1%82%D0%BA%D0%B5-%D0%BA%D1%80%D1%83%D0%BF%D0%BD%D1%8B%D1%85-%D0%BF%D1%80%D0%BE%D0%B5%D0%BA%D1%82%D0%BE%D0%B2.8442/