It's not just great. It's so good that even on much older android phones than the ones tested in those links the brightness of the screen has a larger impact.

This is by design, so that even extremely dated smart tvs and etc can also benefit from the bandwidth savings.

Fun fact: I can't say which, but some of the oldest devices (smart tvs, home security products, etc) work around their dated hardware decoders by buzzsawing 4k video in half, running each piece through the decoder at a resolution it supports, then stitching them back together.