I use a Boox Page 7" ereader. All the big manga apps, including Shonen Jump and Manga Plus, work on it. None of them support the page-turn buttons except Mihon though. The Shonen Jump app is an especially bad experience because you need to swipe to turn pages; at least with Manga Plus tapping the edge of the screen works. Speaking of the screen, 7" is plenty big for reading in your native language, but I occasionally have to zoom in to make out certain kanji when reading in Japanese. It doesn’t sound like a big upgrade in size over phone screens but since it’s actually the right aspect ratio it’s a huge difference.

As for color, I suspect that color e-ink screens aren’t gonna be a great time. You’re giving up effective resolution in exchange for it, and I think I’d prefer sharper black and white performance instead.