Is Hyper Backup to cloud storage a good option for a 4 TB Synology NAS?

Yes, Hyper Backup to B2 is a reasonable option to evaluate. Pairing an onsite copy with an offsite one gives you a quicker local restore option and a copy that isn't in the same building.

Check the cost for the amount you expect to retain, not just the current 4.1 TB. Retention, changed files and restoring data can affect the bill. Also test restoring a few files and make sure someone is checking whether the backup jobs succeed.

Before picking a provider, get management to answer two questions. How much recent data can the business afford to lose, and how long can it wait for a restore? Those answers drive the backup schedule and whether an external drive is enough for recovery.

Also check whether all 4.1 TB needs the same protection, whether there are legal retention requirements, and what hardware would be available if the NAS failed. A cloud backup is useful, but downloading a full restore may take longer than the business expects.

Consider ransomware as well as hardware failure. A connected external drive and cloud credentials accessible from the NAS could be exposed in an attack. Look into rotating an offline drive and whether your chosen backup setup supports an immutable copy. Snapshots on the NAS can add another recovery layer, but they aren't a substitute for a separate backup.

Check what the company already uses to back up its other systems before adding a separate tool. An existing commercial backup platform may support the NAS and could simplify monitoring and managing onsite and cloud copies. Compare that against Hyper Backup on cost and recovery features.