I have 4 6Tb HDDs which I got new from work: been running 24/7 for the last 6 years.
The 4Tb drives they replaced where running for the previous 10 years (bought new as well) and are still in a drawer, got replaced only for the opportunity to upgrade to 6tb.
If your refurbished last only 4 years, to be that is not a positive gain, you lost money. New drives should last 10 years in my personal (and debatable) experience. But I think those drives you bought will last more than 4 years.
I have been far luckier than that all my life, I never had a drive fail on me, and I keep them a looong time.
Maybe once, 20 years ago, a drive failed? Can’t really remember, but probably it did happen. Being on a Linux software RAID 1, just remove and plug a new drive, run an attach command and forget.