I'm currently working on a cross-compilation solution that needed these root filesystems, and knew they would be of use to others.
If it helps with piece of mind, the images are built in the open (the Azure Pipelines YAML file in the repo handles this).
There are a bunch of scenarios in which you may find yourself unable to create these with debootstrap yourself (e.g. restricted permissions, a kernel without binfmt_misc suppport), but are able to use them (using proot to avoid needing admin, or Resin's patched version of QEMU that reworks execve() to operate without binfmt)
