As a product category, the smartphone is singularly bizarre: You buy it for its convenience, then buy secondary devices that prevent you from using it. As if you, the user, have no willpower. The Brick and Unpluq tags on the market will block certain apps, since you cannot be trusted to not access them; Yondr bags are used by venues that cannot trust you to turn your phone off.
Well, here's yet another piece of plastic and circuits you can buy, to avoid having to develop willpower. The Picco, by Chinese manufacturer Boox, is a separate e-reader screen that attaches to the back of your phone.
It then allows you to read e-books, which you could simply do by using the regular screen on your phone. Oh wait a second, no you can't, because of the whole willpower thing. So yes, spend $100 on this additional object that you'll also have to keep charged.
Can you think of any other product category that has spawned a secondary category of objects designed to prevent you from accessing the original thing? The only thing I can think of are those flip-up button and switch covers, or maybe those breathalyzer ignition interlocks.