Often for eInk screens the problem with speed is the driver (either code or chip), not the paper itself. For example, many drivers don’t support partial refreshes.

I just bought the B/W version of this screen and read the data sheet. Internally, it is four different screens. So I think (haven’t yet received it) each quadrant takes about 2 seconds to refresh (2 seconds is a pretty common refresh time for eInk). A better driver could do all quadrants at once for a ~2 second refresh.

Because of the weight of the particles that are being moved. They have to shake them, move them a bit, shake them again, move them a bit again. Moving a blob of plastic takes a lot more energy than what LCD's do: who just moves something like 1 electron per 10000 in the layer between the polarization filters.

The way multicolor e-color displays work is by having multiple size/weight particles that are moved by different field strengths, but require being even more careful (because every field, shaking and moving, will move every particle)

This particular screen is slow even by e-ink standards