I've been reading novels from non-iPhone cell phones with screens around 55 mm for the last 5 years. I've gone through around 80 books so far.

I read mostly in the bus to work. I'm always carrying my phone, a kindle or a paperback book would be a big extra thing to carry along.

One win for the e-ink display would be that it'd be readable in bright sunlight, unlike the active display of the phone.