When cloning a drive an exact copy of the drive including its MBR, or GPT and partitions is created directly to the target location. This means you get an immediate copy including the hard disk structure, cluster by cluster and sometimes sector by sector ( bad sectors included.) A cloned disk or drive contains all the partition structure from the source disk or drive. A cloned system HDD or SSD that contains the operating system can be mounted as a new drive and immediately booted.Please be more specific about exactly what you mean by cloning once a month, and about how that plus backing up a month of work files on USB sticks would eliminate your need for AV products.
With ordinary backup where the entire content of the selected drive or partition are backed up into a file ( known as an Image ) on to the target location, a backup software is required in order to restore the system or data to a previous state or access the files and documents in the drive. As a result the drive is never bootable. The backup software may or maynot reside inside a drive already infected with a virus thus rendering the newly created copy infected again. Thus the file image ( residing on a separate USB or HDD ) will always be clean, yet the machine used as to re-instate the copy usable again, won't be!
With Cloning you dispense with the infected drive or drives 100%, and your system immediately boots without further action.