This is the one I have since about one year.
I took it travelling and hiking (never without a book!), and am satisfied so far. It's actually thinner and lighter than an average paperback. It can be reloaded through an USB charger, like this one , or computer of course.
It uses very little energy (thousands of pages), and with the proper software can display PDF of what you like. Black and white only, but may be next generations will have a bit of color ?