Years ago I flew transatlantic and just before landing I got up and brushed my teeth with a tiny travel set. I still remember all the people looking at me with my toothpaste and brush in hand thinking “why didn’t I think of that?”

Adding to that that you can also easily make a separate WiFi network (tied to a vlan even) for IoT. OpenWRT makes this very easy.

It really depends how you define reliability. SD cards are physically nigh indestructible, but can show failure when overwritten often. Hence for one off backups it’s actually a good alternative. It will start showing problems when used as a medium that often writes and overwrites the same data often.

I would recommend backups on SD cards in an A/B fashion when you want to give a backup to someone else to store safely.