The e-ink market is tiny to begin with, none of the companies last very long, and none of the products are very good relative to, say, the tablet or Kindle ecosystems.
Remarkable is as close as you'll get to stable, open, and not yet bankrupt IMO. It's that, an expensive Japanese model, or a noname Chinese one. I think the UX is going to suck regardless. I had a remarkable for a week or so and then returned it, was too much of a hassle vs cloud everything on my iPad. Still use a Kobo for reading, again in the cloud. The eventuality of these companies shutting down and me losing all my books is worth the tradeoff of day to day convenience for me.
You don't have that many choices, I don't think... just find something you can tolerate and be prepared to export your data out when they go bankrupt.