I have some refurbs in use. I've never had an issue. They've been running for years with no problems, just like my brand new hard drives. But for me, I've been using hard drives for over twenty years and I've yet to have a hard drive die once I put it into service(I have had some DOA or dead from user error, like me breaking the SATA connector, but that was before I put them in service).
I still have a hard drive from the early 90's that is 20MB that I had in an old 8088 PC. That even still works. And 250+ hard drives later, I'm still waiting for a hard drive to fail. Of course I expect it to happen eventually, but so far I've not seen it. And currently I have over 85 hard drives in use in various devices. Although mostly in my WHS and two unRAID setup.
Roamio Pro (5TB Red)
TiVo Mini x4
Roamio Basic OTA (1TB Red)
53TB unRAID2--38TB unRAID3--33TB unRAID1a