An underappreciated benefit of the functional distros (Nix/Guix) for specialized hardware like this is that reproducing the original image (potentially with some tweaks) is very straightforward. For Guix this is just a 'guix system image' with essentially the same 'operating-system' declaration you'd use to configure your system normally; I don't have much direct experience with Nix but I imagine it's fairy similar. Provided you distribute the system config (and I can't imagine you wouldn't), building a slightly customized version of the image should be easy.

By contrast, it is not clear how I'd build e.g. the customized version of Ubuntu that a laptop manufacturer might ship.