Well, with Koreader functioning well on Pocketbook, I think I have made my decision.
I use Koreader on my larger Onyx Boox and it is better than default apps both on Onyx and Kobo (with the added advantage that hyphenation works great with Koreader in different languages).
I went to the department store again and compared the devices side by side (they had Basic Lux, Verse, Verse Pro, and Era on the display) and I am really impressed with Verse Pro. Its e-ink is much darker compared to other devices and the dark mode looks impressive! I am surprised with how good it looks and can't wait to get it.
Also, I found a thread on Reddit with photos of Verse Pro and Kobo Clara side by side, and what I saw confirmed my suspicion about the reflection of light on the top layer of the Kobo screen. Here is one where the difference is the most obvious:
https://www.reddit.com/media?url=htt...8f2135674b3cad