CopyToFlash is a small program which speeds up the process of copying files to multiple flash drives.
The idea is that you first specify the folder containing whatever files you'd like to copy, and where you'd like them to go on the destination drive.
Next, click "Start Monitoring" and the CopyToFlash Drive Monitor window appears, just waiting for you to connect a USB drive.
As soon as you do, the program automatically copies the files to the drive, telling you to unplug it when this is done. And now you just remove one drive, plug in the next, wait for the files to be copied, and carry on until the job is done.
If you're only updating two or three drives then it's probably not worth the effort of launching a separate application; we'd just stick with Explorer.
If you need to copy in bulk, though, CopyToFlash's zero-click approach should make the process much quicker and easier.