Core modules are a bit better laid out, meaning you will have a more unified experience across different dev boards. Additionally, there are more boards that appear to be supported, but don't quote me on it. Things like os/time/filesystem stuff act how you would expect running cython. IIRC the big selling point is anything that you can run on CircuitPython you can run in cython, whereas with MicroPython some of the OS and time functions act differently, so might not work without code changes.