Just a question of adjusting brightness properly or setting up a theme that suits you. I can read comfortably in bed in the dark using a light on dark theme at 2% brightness as well as in the garden in full sunlight. And no issues with eye strain.
I have a Sony reader but it hasn't been out of the drawer since I bought a tablet. I'm afraid that for me it's a no-brainer and I suspect the dedicated ereader will go the way of the netbook before too long.