BTW, I mentioned I was a fan of the Plugable caddy, and was asked for the link. Here it is:
http://plugable.com/products/usb3-sata-uasp1
These folks have good support and good prices; way better than so much of junk I've been through over the years.
I wouldn't recommend the caddy for extended heavy use, mainly due to heat. But I've left a drive in for my regular TM backups, which don't require much access to the drive, so heat isn't much of an issue. The utility comes in the ability to swap out.
Everyone's backup needs are different. For me, theft is probably the biggest hassle after drive failure. This caddy makes offsite and secure storage easy, and easy is important. Otherwise you won't get around to it, and you're hosed.
And I'm not sure anyone mentioned it, but a second computer can be part of a backup plan. It removes the need for a clone, which you should have since being computerless can be a big problem. And drives attached to, or within, that second computer can be used for backup as well as serving files. Some find it as easy to manage as a NAS setup, and it certainly is a good use of an older computer. I have a G4 with Snow Leopard that's still doing that duty after all these years.