The text will be better than a real mono 150dpi (Kindle DXG, Inkpad Lite) , but never as good as real mono (no colour filter) 300 dpi. How much better than 150 dpi will depend on viewing distance, your eyesight, reading glasses if required, font and what method of sub-pixel addressing they use (if any).
It might look better or worse than a 200dpi P10, depending on viewing distance, your eyesight, reading glasses if required, font and what method of sub-pixel addressing they use (if any). It will look better than a 200 dpi (finest mode) fax because that uses only black or white, no aliasing on curves/diagonals using greys. It might even look better than an ancient 300 dpi laser print, as those had fixed dot size and no greys. Most mono ereader renderers seem to anti-alias diagonals using the 14 grey levels which can make 300 dpi eink mono comparable to 1200 dpi laser text.
See
https://en.wikipedia.org/wiki/Spatial_anti-aliasing
Explains how having greys improves the apparent resolution on curves and diagonals. Vertical and horizontal elements are unaffected, so some kinds of images purely in black and white with no greys look just as good on 200 dpi fax as 200 dpi eink and will look better on 300 dpi ancient laser prints. But images with diagonals curves or greys will sometimes look far better on 300 dpi eink than a 600 dpi laser. Some inkjets and lasers can vary dot size so as to get more shades on a denser dither.
See also
https://en.wikipedia.org/wiki/Font_rasterization
Somewhere I have books I used as references to write graphics drivers for games during 1992-1996. Early 3D games actually used purely 2D techniques. It's a very complex subject and most of the related patents are just gaming the USPTO because the techniques known decades earlier. Of course for older games you pre-rasterised the fonts needed for the resolutions needed to save CPU and space. Sub-pixel addressing was known but not used as it doesn't work on CRTs (monitors or TVs). Any LCDs were rare, low resolution and mono in 1980s.