SyncBack PRO here, been using it for years
Basically I set the source and the destination as my external USB drive and within seconds it finds the differences between the source and the destination and copies or deletes the data from the destination to make them a perfect match. You have to select MIRRORING s the backup type to have the contents of the destination be matched with the contents of the source
They also have a free version that does the same thing but with a few more options, does the job as well if you ask me