I spent a week trying to read most of the books I wanted to read on an iPad, to save carrying several books.
eReaders are good for novels, news, anything simple you want to read more or less linearly. But when I want to do serious reading on a topic, and especially a difficult topic, that involves flicking back and forth between several books open on your desk on the same subject, jumping back and forth between them and between different pages of the same book. The iPad doesn’t work very well for that. A large computer screen is better for handling the nonlinearity.
When I used to use the visual editor vi years ago, there was a way you could mark certain sections of the code and jump back and forth between your current location and a previously marked location by hitting one key (my fingers want to say it was two single quotes typed quickly). Some quick context changer like that would make reading nonlinearly apppreciably easier.