Some tech gurus predicted that the tablet computer, with its versatility and color screen, would kill the stand-alone e-book reader, with its focus on books and its black and-white screen. But Consumer Reports’ Ratings reveal the e-book reader has endured, even thrived, by providing an increasingly optimized book-reading experience at steadily lower prices. Most of the rated models, new and old, are lighter and easier to read than tablets and have much longer battery life.