Not the GP, but have you ever tried using a laptop outside, especially on a sunny day? It's not terribly pleasant, and you'll probably be squinting the whole time - the reflective surface is particularly troublesome.

I haven't tried a large e-ink display (though I'd love to, especially for coding), but I've been using Kindle e-book readers for years - the difference compared to a glossy, or even matte, Led display is incredible; it's just like reading a printed book. No squinting, no eye-strain, just really pleasant to use.