I’ve always relied on multiple aspects for my used drives (currently ZFS raidz2 which itself provides multiple checks, but I also do backups of the really important stuff). It doesn’t matter though, all drives new or old are going to fail and you just have to be ready for it. The worst case is multiple drives failing at once, and I had that happen several times when using a weak power supply.
So far I’ve been really happy with the refurbs from Amazon though, plus the NAS is nothing to sneeze at. I upgraded the server to a newer machine, then realized that allowed me to step up in families for my SAS cards. Basically went from a machine that could push data at 70MB/s (and was constantly behind) to a new machine pushing 450MB/s or more with almost no lag. I run a lot of stuff on my home network so it’s been nice having the new speed, and the zfs pools are providing around 92TB on one set and 22TB on another set so I have room to go crazy. If I had to buy new drives I’d have maybe half that amount of space.