[fermienrico]

Yep, I really like how the bootloader works - upgrades are drag and drop. I'll write to Paul if he is open for selling the bootloader license to me for commercial use. I am sure we can come to an agreement.

[detaro]

He sells the chip pre-programmed for the older versions: https://www.pjrc.com/store/ic_mkl02.html

Support for the chip used in Teensy 4 is apparently coming in the near-ish future: https://forum.pjrc.com/threads/57132-Bootloader-Chip-For-Tee...