Caddies are much of a muchness - IMHO aluminium ones are better from a heat point of view. I use caddies myself for both of my hard drives.
BUT - for a backup drive I use an external USB unit - it's far simpler to plug and unplug when needed than a caddy.
AND - I don't clone, I image4 - which is just as straightforward as cloning in the event of failure (though it takes longer), and uses significantly less drive space. It means I can get three full images (grandfather, father, son) on my backup drive - plus a daily data backup.
AND - it makes no difference what make of drive you use. You can use a small lightweight 2.5" drive, which needs no external PSU if you like.