I’m not sure I trust some of this.
They want you to re-symlink your /bin/sh to /bin/bash and install some tools on your host system. This is not a clean process.
I’ll be using a chroot instead using schroot and debootstrap for a little bit of sanitization. I don’t like that this was not mentioned at all as there is no telling what features are used by non-bash shells. For instance, in Ubuntu Xenial, /bin/sh is symlinked to /bin/dash which may have features in use by system scripts that only exist in dash.
Assume it breaks shit until you know. These builds that are being bootstrapped need to be clean.