It seems this HDD is on Black Friday Special, a few bucks more than during Prime Day, but doesn't seem to be a Prime exclusive.
These likely contain a HGST Ultrastar DC HC520, which is a $600 drive if you want to shuck it.
Better to shuck these than the Elements, as these have the middle screw holes missing from the Elements drive.
Edit: Quantity limited to 3 per account. I tried ordering a second lot after it came back in stock and it would not let me.
Edit2: Seems this keeps going in and out of stock throughout the day, so I think it's best to leave it until end of Cyber Monday so people can keep checking if they need it. I'll set expiry for Tuesday 1st December.