Looks promising. I've watched some videos of them now, and checked out their website.
https://mytolino.com/compare-tolino-ereader/
Seems like I can't use it for maths, as there's no stylus yet. But they write they have water protection by HZO, meaning any producer of rink tablets could get the same, if they just got in touch with HZO.
Seems like I am pretty alone in wanting to read near a beach/sauna/jacuzzi/pool wherever there's water and/or humidity. Toledo is onto something, but the others not.