“We reduced the energy required by a factor of 5 (compared to stock Debian at 9.5 Ws until user space).”
A Pi Zero 2 W running stock Debian takes 8 seconds before Linux prints a single line. A custom Buildroot image reaches user space in under 3.5 seconds, with only about 400 ms spent in the kernel. The Raspbian kernel weighs 25 MiB against 8.5 MiB for the trimmed one. Most of the boot was never work, just distro bloat nobody bothered to cut.