"It seems like a waste. Double the screens and you halve the battery life and double the cost. Since you can only read one screen at a time it seems wasteful and pointless."
Nope. An e-ink reader doesn't use any power to display a page, only to change the display on the page. It would only use more power if it were backlit. In any case e-readers can last for days or weeks without needing to be charged, even with a backlight, so it's not that much of an issue.
Besides "wasteful" and "pointless" aren't necessarily related. Yes it might be wasteful to have 2 screens when 1 will do, but it's not pointless if the reader gets a better experience.