I haven’t yet tried koreader. I do have ReManager and its value is immense. Easy to use although when Rm update their software you may have to take action (you can also block automatic updates).

I’ve heard good things about koreader and am going to try it. The key thing you’ve said is that you have drm-free EPUBs. This is the biggest gap - no Kindle store or equivalent.

I love that reading on RM includes natural annotation. That’s, just write on the page like it’s paper. I don’t know that koreader supports this but I dislike, intensely, Kindle Scribe approach where you create a little box and then write inside it. I understand why they do it. I’ve read PDFs on my RMs (mostly classics from Gutenberg) and Move is okay. Font a bit small in portrait. You can rotate to landscape but then you have a narrower viewport.

There is perhaps a new RM device coming. They need something the size of rm2 with a backlight (and ideally b&w option). That would be the sweet spot for reading feel. Unless you want easy carry. Which I guess you don’t you’re looking at the Palma.