I see reMarkable says[1] you can use it without a subscription, but I'm not confident they won't pull the rug under my feet.
[1] https://support.remarkable.com/s/article/Using-reMarkable-wi...
The keyboard folio was also better for the RMPP since I often experienced loose contact with the one on the BTUCP when I used it on my lap (flat surfaces were good once I set it up). Otoh, the material used in the BTUCP was much better since the RMPP one uses a polyster weave which often leaves me with slight goosebumps. Additionally, the keyboard folio isn't a feature I use often.
I really can't talk about the others so for all I know, Scribe or supernote might be a lot better. RMPP does have a 90 days no questions asked return policy if you want to try it out (though I'm not sure how much that's worth).
That being said, my girlfriend loves her Supernote too, so there's plenty of alternatives.
Thanks for mentioning these other devices. I used to have a Kindle Paperwhite (I see it is different than Scribe), butI lost it. I'll explore the other options.
I'm a sucker for high-quality materials and thoughtful aesthetics. Metal / glass over tacky plastic.
Being an "excellent offline device" also matches one of my core requirements.