And not to thread sit (but since we're the only two people here right now) let me re-add a point which I removed from the OP because it was a hair over 2000 word limit--I bought the DPT-RP1 to read research papers, technical books, and non-fiction/text books at 100% size.
Responding to your comment about suggested marginalia set, its not intended for every type of text. But in the above mentioned context, the tags I introduce in the document (q, r, t, d) when performed with a grep search on plain-text files I have for notes on these technical books, I can generate quotes, references, terms, and definitions for over ten years of reading in under 5 seconds. That's darn useful.
Adler and van Doren begin their book with the importance of defining terms. You can't understand a book if you don't know the terms the author is using. I would argue that universal to all texts. The Kindle has a great dictionary feature which supports this idea. When it comes to technical books though, many terms are not defined in the standard dictionary.
For paperbacks, I use a Kindle Paperwhite, and that's a great product if you don't mind the MOBI format.