Well... you get to reproduce yourself and run everything covered by the gplv3 (same exact versions, same binaries even with Nix) on the device. You get everything you need to reproduce the device's rootfs. It will boot your image, if you disable Secure Boot. You can install your own UEFI certificates if you want to enable Secure Boot with your image. You even get the complete development environment for free (Nix).
Our IP is obviously not covered by the GPLv3.
What is the problem?