In duo mode, I can have two drives backing each other up, and feel very secure that my family photos, important documents and video archives are well cared for, with identical copies on two hard drives. Other WD models are network devices, which you might consider, but know that they can take longer to do a full backup, or you might not have a home/work Ethernet infrastructure. Plus, as a USB device, you can backup on a regular schedule and leave this OFF your network to eliminate the risk of hackers getting all your important files. I like that the hard drives are individually replaceable, should one ever fail. The key drawback is that with USB, you have to be the one to discipline yourself to back up regularly, unless you keep it connected all the time.
I would recommend this to a friend