In addition to what you point out: If the IPS panel is on while you read on the E-Paper screen, there will be light aimed at your eyes from the left side. That

In addition to what you point out: If the IPS panel is on while you read on the E-Paper screen, there will be light aimed at your eyes from the left side. That alone will cancel out a good deal of the benefits of reading from a reflective screen. Similar to using a regular display against a daylight lit background, such as an open window.