Cloning programs are all pretty much the same, save for different user interfaces. They all do the same thing.
While 10GB "is enough" for an OS partition, it's only enough if you don't load ANYTHING else. Such as Office, 3DMark, Games, etc. If you put every single other program and application on another partition, then 10GB is fine.
With patches, security updates, etc, Windows DOES grow over time. Plus, you need to have empty space in order to defrag.
Personally, I put all my programs on the OS drive. My Documents, Games go on another partition.
What I do after a fresh install: Apply all the latest patches and security updates as well as device drivers. Defrag. Reboot. Make an image of the OS.
Now I have a perfect copy of my OS install, current as of the date it was made. Re-imaging the OS drive takes all of 10 minutes. Doing a fresh install and patching takes an entire day.
IMO 15GB is OK, 20GB is perfect for the OS drive.