I would add that I had possibility to get and use Kindle DX for free! And I refused as it was unusable for my needs. Instead I bought M92 almost year ago and I've never regreted this decision.
I loved M92 from the very beginning... So, my opinion may be biased.
But of course, if you want only read and have up to 50-100 books or documents Kindle DX will do the job just perfectly. If you need more, M92 is worth considering.