Using file-level archiving tool will not preserve the bootability of a USB Flash Drive nor will it preserve the filesystem specifics and layout. Depending on your needs, this may or may not be important.
I haven't found a UFD imaging/cloning tool that I'm entirely happy with, but you could try this free tool from HP:
HP Drive Key Boot Utility
It will allow you to backup the UDF to an image file and also restore an UFD from the same image file. Unfortunately it saves everything including unused sectors, so the image is as big as the entire drive. IIRC it also doesn't allow you to restore to a drive of a different size.
In case anyone thinks that WinImage would be the ideal solution, my testing indicates that v7 does not preserve the filesystem specifics and layout of the saved UFD drive reliably enough to guarantee bootability after a restore. I'm not sure if WinImage v8 has solved this.