I can't speak for the Kepler Pro. But I have a Boyue T63 - 6 inch display, 300 dpi, flush screen, and expandable storage. Its build quality is good. I've seen the Voyage. The Voyage might have a slight edge in build quality and overall screen quality.
The Boyue, like several of the other options mentioned in this thread, runs Android. So, you can install some reading apps. Kindle and Nook do not work that well on devices like these. However, Moon Reader Pro, KOReader and AlReader (to name only three) work just fine. The Bpyue has its own reading app, which is good enough.
I mention the Boyue because, of the e-Ink devices I know about, it comes closest to what you are looking for.
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