I personally quite like the approach of using the bootloader chip as light DRM: The majority of the value is in software you can freely use, with licenses provided. Prototyping with a Teensy and then making a product using the same parts and the libraries, not a problem. Just if you want to provide the same easy dev-board experience you need the bootloader chip (which you can buy and use for your own design) or invest your own development of an alternative.