I've spent the last few weeks really digging into the Xteink X4, a miniature e-reader that fits onto the back of your phone. As I expected, this $69 e-reader wasn't the best e-ink device I'd ever used, but neither was it absolutely hopeless. The Xteink X4 is now a must-buy for keen readers of every stripe. The Xteink X4 is now an excellent e-reader, and it's easy to recommend itI wasn't expecting much from the Xteink X4's software. I always have my Xteink X4 in my pocket, and I can dive in to my books whenever I have an idle moment.