That's all I wanted it for, that's all it does. And most importantly - it's priced like that's all it does.
But they seem to get equal or better battery life out of the Transflective LCDs currently used, which operate on a similar principle as e-ink, in the sense of how the light reaches your eyes:
https://en.wikipedia.org/wiki/Transflective_liquid-crystal_d...
I now pay for gas, small groceries and various other things with my watch. I unlock my computer by just pressing the spacebar instead of typing my password. The killer app for me is when I'm cycling or motorbiking and have directions appear on my wrist instead of my pocket.
Hence I charge phones and laptops during the day and only when someone is around to supervise.