I've got a number of e-books on my Kindle and for me text books don't work well on that.

If they are explicit Kindle books then you can at least navigate to the table of contents and then on to specific pages.

If they are PDFs then navigation just doesn't work. You can't dip into the book as you would with a physical book. This means that you can't stumble across content speculatively.

The Kindle format translation service doesn't like PDFs.