Urbackup - Btrfs vs ZFS pros and cons?

Thanks to for zfs support for docker.
I’m just a bit confused because different info at https://hub.docker.com/r/uroni/urbackup-server. On one side you have the special Tag latest-zfs and at the run example you use the Tag latest and use for zfs support the arg --device /dev/zfs.

do we need for zfs support setup both Tag and Arg or is only one of both needed?