I would run 2 or more parity disks always. I have had disks fail and rebuilding with only one parity drive is scary (have seen rebuilds go bad because a second drive failed whilst rebuilding).
But agree about backups.
But agree about backups.
If your odds of disk failure in a rebuild are "only" 10x normal failure rate, and it takes a week, 5 disks will all survive that week 98% of the time. That's plenty for a NAS.
Hence the first sentence of my three sentence post.
So I made a simple comment to point out the conflict, a little bit rude but not intended to escalate the level of rudeness, and easier for both of us than writing out a whole big thing.