I'm someone who had them during the boom around 2010 or so, then found myself giving them away because they didn't seem useful, and now find myself wanting them again. Mostly I've noticed how I like to read in bed at night rather than on my phone, am not happy with the illumination options with real books in that situation, and not happy with the screens on my phone either.
I'd probably buy one immediately if I could be guaranteed I could put any pdf on it and have it display flawlessly, and if it were relatively open in terms of compatibility.
I'm getting a lot of use out of my ancient Sony DPT-S1 for this purpose. It has a huge screen but is very light and well-balanced so holding it for long periods is not a problem for me, compared to holding a similarly-sized lcd tablet. I've converted most of my epub ebooks to pdf (thank you Calibre) just so I can enjoy reading them on this device.
I got one too and they really rock! I read papers on them mostly and the odd text book. I had a Kindle fire reading novels but have last it recently. I'll maybe take a sieve or of your book (ha!) and try converting everything to PDF, but I really like the built in dictionary on kindles. just wish The DPT-S1 was open to writing your own apps for, I would have done it by now.
I'd probably buy one immediately if I could be guaranteed I could put any pdf on it and have it display flawlessly, and if it were relatively open in terms of compatibility.