@Binder It's not iffy: it's flat-out lying. Older Reds were CMR, but they updated the smaller drives in the lineup to be SMR without substantially changing the model numbers. Amazon currently sells:
"WD Red 6TB NAS Hard Drive - 5400 RPM Class, SATA 6 Gb/s, 64 MB Cache, 3.5" - WD60EFRX"
and
"WD Red 6TB NAS Internal Hard Drive - 5400 RPM Class, SATA 6 Gb/s, 256MB Cache, 3.5" - WD60EFAX"
The former is a good CMR drive. The latter is trash SMR.