This ends up being a hassle unless you are using exactly the same OS on both sides, since you need to either have the right version in ports/apt/pacman/whatever or manage the Unison builds yourself.
https://github.com/bcpierce00/unison/releases
But I have seen problems when one version was far ahead of the other
> Unison 2.53.3 (ocaml 4.12.1): Contacting server...
> Unison 2.51.5 (ocaml 4.14.0): Contacting server...
restic is specialised for backups and offers uni-directional backup and uni-directional restore from backup.
unison implements bi-directional sync.
if you don't want bi-directional sync and don't want specialised backup support, rsync will get the job done.
if you want bi-directional sync (unifying changes made on both sides), that's something that neither rsync nor restic can handle.
tangentially, re: using restic for offsite backups, one storage provider that pairs quite nicely with restic is rsync.net -- they have a lower-rate pricing offer specifically for use with restic (by default rsync.net filesystems have ZFS snapshots available, they disable ZFS snapshots for these "restic accounts" -- the restic application is then responsible for managing backup snapshots, not the filesystem).