Before you go this way, make certain you have an opportunity to view the graphics/diagrams on your electronic reader of choice. Typically images and tables do not translate well. I've no experience with the Nook so perhaps this is less of an issue, but check it out.

Personally, if I thought I might need the books later on I would spring for the real book. I gave my first Sony Digital Reader to my sister when she was still in RN school so she could use it to study for her RN test. This was a massive book they had made available in PDF format. Between the size of the screen and how the tables and graphics rendered, she finally went back to the real book.

That was a couple of years ago and eReader technology has moved on quite a bit since that time so you may find it a different experience.