I have one, and Armbian has an official release for it and works quite well with a Kioxia 512GB NVMe.
But at this moment I’m just saying there are similar boards out there, and the 5 Plus might be slightly cheaper (no wireless though). Radxa also has a similar board based on same SoC but only has one GbE port and price might be similar to the Banana Pi.
The competitor is the Orange Pi 5 Plus, also has 2x 2.5GB Ethernet, same SoC, more USBports, no integrated WiFi+BT (optional M.2 module), eMMC connector, M.2 NVMe socket (up to 2280).
If your backups are visible from the targeted systems, you are doing it wrong. Done right, a backup utility at most only uses an agent on the systems to be able to contact them to get the data and the backups are not reachable.
Have a look at how BackupPC works, not even an agent, it accesses network shares to get the data: