Storage boxes have limited connectivity to 10 simultaneous connections, they are mostly for backups and internal usage of servers.

Storage shares are nextcloud instances with 100 simultaneous users and better connection. These can be used for UNA too.

But imo for UNA storage their best offer would be their 16 TB SATA Enterprise Hard Drive € 20.50 euro/month. Of course all these needs your own dedicated server. (you may have your own physical dedicated server as low as 37 euro/month with quite enough hardware https://www.hetzner.com/dedicated-rootserver/. Currently I am using 2 of the AX41 NVMe with additional storage boxes for backups)