I just use nbd-server, nbd-client (kernel module nbd). While at home things are fine, when not at home things can get bad unless you use something like UDPspeeder <https://github.com/wangyu-/UDPspeeder> then you just need to deal with slower speeds.
I do backups with borg while connected to the NAS with ethernet.
> While at home things are fine, when not at home things can get bad
What does "bad" mean exactly? Unrecoverable errors / faulty writes? It might be an irrational gut feeling on my part but for some reason operating a block device over a network makes me feel uneasy. How easy is it to mess up one's data?
NBD uses TCP. And I had no unrecoverable (journal) corruption happen.
Imagine you had a physical drive which had unreliable reads and writes but that would always go through eventually. In that scenario I believe you would just have abysmal latency as the OS keeps retrying - and if the latency between retries was in milliseconds the actual speed would drop next to 0.
That said, sudden unrecoverable loss of connectivity would be equivalent of yanking out a physical drive. You would want to use a journaling filesystem.
I do backups with borg while connected to the NAS with ethernet.