I think too he mentioned he has sources.
I tried to write my own firmware, but failed due to underestimation of effort and lack of knowledge of stm32. I thought I'd write a basic firmware in a few evenings, but failed even to get LCD working :/. Then I realized that I don't know how to control the main IC, and its datasheet was uncomfortably big.... So, many things it seems need to be implemented from scratch, it's not like an arduino-style development when all it takes is just install libraries and bind them all together in main().