Actually latency is way less of a problem, if the input is buffered, as you can just type ahead.
I meant "time between input and visible change on screen", or lag between writing on a tablet and the screen or eink showing the drawn line. It's not really as crucial when typing, but especially for writing or drawing on a tablet low input latency is the difference between getting in a real flow state or not.
E-ink has had some improvements- I'm acquainted with the developers of this project: https://www.crowdsupply.com/modos-tech/modos-paper-monitor
Refresh rate is only one component of the system- an integrated display controller can lower the latency, and of course, the choice of computer affects the speed as well. Their choice to go with USB-C Alt is a good idea.