@NebulaTide what’s the threat model? If all you care about is privacy of your data, ZFS encryption may be sufficient. If you care about privacy of things like dataset names, how often you create snapshots, properties and their values, ordering of writes to various datasets, etc., then you want full disk encryption. Perhaps your threat model requires both types of encryption for the most privacy and compartmentalization.
This has nothing to do with FreeBSD, it is common to ZFS on all platforms.