Well, their release is essentially Debian Jessie with a few defaults modified (have the "init" meta-package depend on sysvinit instead of systemd), a few packages removed (systemd-sysv) and a few packages rebuilt to not depend on libsystemd (to no longer optionally support additional integration under systemd for freedom reasons).

Keep in mind that they originally wanted to release their version on Jessie in early 2015...