The help states there is an option to compare this on incremental backups, but it is not there. Is it done automatically now, or not implemented?
Incremental Backup - Comodo BackUp will compare files in the source and destination directories and will copy changed files only. This will help you to speed up backup process if you execute a large backup. By default Comodo BackUp will compare attribute “Archive” of the files. It is more effective, but only in case you are sure that no other program is working with the same file (e.g. another backup). But if you have any doubt about it, it will be better to check both - "Check attribute “Archive” and “Check size and time”.