I see some fairly interesting prices for refurbished drives on Amazon, 35~40% cheaper than new. Example here: 16TB Seagate Exos X18 Refurbished at 166€ and New at 260€.
I am considering this option for my home NAS, running with BTRFS RAID10, plus important files are backed-up to a cloud storage, but not my media collection.
In your opinion, how risky is it to use refurbished drives ? Do you have to good or bad experience doing so ?
Seems fair compare to the discount. What tool can you recommend for testing the drives ? Do you have some programs that are available on Linux ?
SeaTools is a long-standing, trusted tool for HDD testing. I always have a bootable drive with the SeaTools bootable image on me for diagnosing hard drives.
https://www.seagate.com/support/downloads/seatools/seatools-legacy-support/
Keep in mind that testing a failing drive will likely make a failing drive worse. For your use-case this is fine, but for anyone else looking to test drives, please create a backup image of the drive prior to testing.