From the abstract: "It is not the technology itself, but rather the image quality that seems crucial for reading."
In other words, it's what I've been saying for years. The important part is not the technology (eink vs. LCD, front-lit vs. backlit), but the resolution as in dots/pixels per inch. Eink has "fuzzy" pixels, and so gets an artificial boost to ppi despite being relatively low, though the new 1024x768 6" screens have finally cross the 200ppi barrier. Anything over 150ppi is comfortable for most people, which is why the iPad pre-retina display was bad for reading but the Nook Color was good.
Back light vs. front light vs. reflected light is a red herring.