Been around for years. They use e-ink displays, so they consume no power while not updating. Most have a little barcode to identify the display to the system, so you can scan the tag, then set the contents.
Seeing as supermarkets by them in the 10's of thousands, the unit price has come down a lot, and now you can get the display unit on ali express for a couple of euro. Various maker friends have used these displays for things like a panel with live departure info for the local tram stop. Or a dashboard type display for their home, showing which windows are open, how much power they are using, temperature, etc...
Great bits of tech. Highly recommend.
J