It can do any of the above
It can work on device label, device serial number or drive letter, depending on what you want and what the removable medium supports.
I have 2 CD keys that trigger different backups (one data, the other key apps installs and license numbers), and 2 DVD-Rams which again trigger different backups...
This is not a super-slick pro-looking tool - figuring out how to pick file sources and targets took a few minutes puzzling - but it has a lot of features for the price, and the "no hands" feature is peace of mind. I love the fact that I can just tell my mum when i call her "put the usb stick in the computer" and I know it does a backup of all her files (that one is set up to keep 3 backup versions in parallel, should allow to recover from any disaster at mom's)