MacRumors posted a review on the Prynt Pocket
A quote from the article:
Prynt Pocket, priced at 150, is a portable printer that's designed to work with the iPhone, allowing you to print small 2x3 photos wherever you go thanks to ZINK paper, which does not require printer cartridges to work.Prynt Pocket Review
There are several of these iPhone-compatible miniature printers on the market, but the Prynt Pocket is unique because it's designed to connect to the iPhone using a Lightning connector, a feature that has both benefits and downsides.