[Quoth]

In my experience especially the House of Random Penguins and inmates.

I don't need a lighted case as I don't use front lights, but for just reading the KK3 beats the later Basics (till 2022 model) and others before the PW3. As does the old Sony PRS-T2 (SD card slot, touch and buttons, T1 inferior).
I did replace the battery in a second hand KK3 which I still have.
Another good old ereader if you want small at same total resolution is the Sony PRS-350. The two Sony models allow Calibre to do collections, though I use the custom column used for Kobo rather than default tags column.
A decent small current model ereader would be the Y-Ben P47L.

However the S/H Kobos give the best Calibre support. I think all touch models except mini have fairly up-to-date firmware and thus support series as well as collections. Kobo is better for Annotations/Proofing work flow than Kindle and better control of margins & line spacing.

All our ebooks render almost the same on KK3 in azw3 as in epub on other ereaders. Only the mobi only Kindles are inferior. The KK3 was mobi only when I got it till I updated the FW.