[Quoth]

If you like the original H2O (I had one) and want notes, then an 8″ Kobo Sage is good. Better than the Elipsa for notes. Better screen than Kindle PW3 or PW4 or Kindle Oasis 2nd gen.
I did have KoReader on the Elipsa for a while, but not needed now.

I have a 6.8″ Android eInk (Mobiwave is Android) and it's only advantage is able to run Library / subscription apps. Even with KOreader, it's poorer than PW3 and much poorer than Sage to read ebooks on.

I'd never heard of Mobiwave so I looked it up. It uses the Wacom EMR pen (as does Kindle Scribe and reMarkable). I prefer the Surface /MS compatible Kobo pen. I had a reMarkable and gave it away. Also gave away the Oasis.

If you are mostly reading bought and PD ebooks, then the Sage is better than Android (it does allow KOReader, but not needed) and allows Overdive based libraries. If the Android on Mobiscribe Wave allows non-playstore APK then KOReader will install. Also if you mostly read subscription and non-ACSM library and Playstore works then the Mobiscribe Wave might suit better as you can install the proprietary Android app for the service.

EDIT
Also all Android use MTP. It's slow and tricky compared to USB Mass Storage (Kindle and Kobo). I've many Android apps and devices and none work as well with Calibre as Nook, Kindle, Sony (not DPT models) or Kobo. The Kobo is best and Sony (only eReaders and all long gone) 2nd best for Calibre.