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.
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?”