If you’ve ever seen an OG Pebble, you’ve seen that display. It looks like a better resolution gameboy display. Very little space between pixels.

Some models are different, though, and basically turn into a mirror when their pixels are turned on, rather than become matte black.

Adafruit sells a dev board for 25 bucks. Perfect for low power wearables, much better than E Ink.

I disagree that memory LCD is better than e-ink. Although, mLCD can do colors and better refresh rates but the colors are washed out, in sunlight grayscale e-ink is much much more readable in my opinion. mLCD also consumes more power in certain cases which isn't ideal.

Is this tech relatively new? Is it merchandised as "memory LCD"? I would like to know when searching for e-reader displays in the future.

It is not new and rarely mentioned in advertising or product information. The memory LCD I've seen are too small for a normal e-reader but if you are doing a large production run you can have something custom made.