It doesn't require NT 6 kernel calls
It doesn't dynamically link against hundreds of thousands of lines of ugly corporate-backed C code you can't read
- Our addon is only a couple or few hundred lines, and libschrift is less than 2,000. They're compiled together.
  The original Allegro_TTF is over 1,000 lines (for a good reason) and has a relatively massive dependency weight (for a stupid reason).

Caveats:

Pre-stretching is not implemented.
The entire caching system is gone, fonts are baked to textures immediately and no further. This makes supporting some languages with this add-on inconvenient, or impossible.
If your usecase doesn't need every fancy rendering feature and can use schrift, you probably aren't supporting enough characters and languages to need on-the-fly caching, so we consider this an acceptable tradeoff.
- The cache_text setting in allegro5.cfg is now reused to determine what glyphs can be rendered at all. skip_cache_misses has no effect.
  When cache_text is undefined, the Latin, Germanic, and Romance alphabets will be generated by default. (not necessarily 32 - 255)
- TODO Alternatively, the developer can force a custom range of unicode characters to be generated using a new parameter in the al_load_ttf_font function.
Kerning, per-character advance and offsets, and other features which are exposed by libschrift are not currently implemented, but doing so is possible. See the above comparison screenshot.