Well, I didn't know there were many manufacturers doing it, but from what you just said I'm guessing that they're all just some random Chinese factories. With high-end products like the Pyramid Flipper we're looking at some more well-known manufacturers such as Samsung and Sharp, not only because of their long-term experience, recognition and established quality standard, but also because we need other stuff to work with their panel, most importantly, Wacom or Ntrig pen technology.
You said Xiaomi produced a phone with it 5 years ago - but wasn't that before the bankruptcy?
Well, after all, it seems like transflective displays are facing the same barrier as e-Ink: big brands are happy pushing forward their beat-the-sunlight super bright LCDs for outside usage, just like LCD-enabled tablets are advertised for reading, because it "just works" since customers have no other choice and they just don't want to invest into moving to a different technology. It doesn't matter to them that eInk is far superior for reading due to amazing battery life and reduced eye stress, or that transflective displays are superior to LCDs outside, as long as there is no competition offering that.
By the way, when I say that eInk is facing a barrier, I'm not missing out Kindles and similar stuff, but I'm just acknowledging that the market just isn't mature and there is a lot missing from it. Basically all the e-readers you can buy nowadays have non-color screens (or LCD but that doesn't count) and quite limited functionality. Oh, and they're way too easy to break because they're using very thin glass panels.