For a long time there have been 2 sectors of the hard drive market.
Domestic drives, which offered good value for money, but were not specified to run 24 hours a day, and increasingly had lousy warranties, often just one year.
Enterprise drives, which were specced to run in servers, RAID arrays and the like, had 3 to 5 year warranties, but cost significantly more than their domestic counterparts. They could cost double or 3 times what a basic drive would.
WD has spotted the gaping hole in the market, those of us who want to build a small network attached storage unit, but didn't want to rink putting cheap drives with their 1 year warranties inside.
Hence the Red series. These drives are specified to be used in NAS devices, with a 3 year warranty and - it's claimed - improvements to the hardware to increase life expectancy. The price premium for the Red series seems to be about 20% above the domestic equivalents, which, if they deliver, seems reasonable.
So far I've installed 1 2tb drive with no problems. Let's see how reliable it proves to be, but Red seems to be just what many of us have been looking for!