My girlfriend is quite happy with her second-generation Paperlike Pro. There is apparently now a third generation[2] with higher resolution.
There are some disadvantages (of e-ink in general). It's not fast – the mouse cursor feels laggy, but typing is OK. You might have to tweak various appearance settings to make things look better in black and white – they have software to help with this for Windows, but not for Mac. Lastly, it's not particularly cheap.
Dasung do mention programming as one use case and demonstrate it here: http://www.dasungtech.com/sta/en/type.gif
They say it's "nearly as fast as LCD". It has different modes to choose from, with different trade-offs between speed and image quality. And the new generation might be faster that the one I used.
Here is a 13.3 inch e-reader which you can also setup as a secondary screen (HDMI input), and connect to any computer as an extra screen: https://www.youtube.com/watch?v=1J3oemOfPlk or https://www.youtube.com/watch?v=sCnPMKvXWas So you are getting both a fully-fledged e-reader and an extra screen.