I have an E-ink machine, have had for over 2 years. I recently got an Android phone and put FbReader on it, and using it for small gaps of time when I never had the full size reader with me.
Suprisingly, I've never picked up the E-Ink reader for over 2 months now.
Much longer and it goes on Ebay.
My reading patters have me reading several times a week, fir 30-90 mins per session. Eye strain (I'm 50 with glasses) has not been a problem.
The convenience has won me over.