I bought one just this week because of this. They really went above and beyond:

- mechanical CAD, schematic and PCB files: https://docs.teufel.de/download/MYND/Open_Source_Hardware_Fi...

- firmware: https://github.com/teufelaudio/mynd-firmware

- Bluetooth API documentation: https://cdn.teufelaudio.com/image/upload/v1748589486/product...

- battery repair/replacement guide: https://cdn.teufelaudio.com/products/MYND/pdf/Teufel_MYND_RM...

I believe that they designed the mechanical parts to be 3D-printable as well.