well, the VNC1L is a USB microcontroller interface, you can change it's default functionality by updating it's firmware. There are a few firmwares, but most of them ONLY allows one USB port with BOM capabilities (you can connect only 1 usb pendrive to the VNC1L)
the VDFC firmware allows to connect up to 2 BOM devices (you can connect 2 pen drives to the VNC1L)
the vnc1l firmware make a USB Device (like a pendrive, or others, like a mouse, keyboard,etc) to interact with another microcontroller (like an AVR) only with SPI or USART communication (and not bother with complex USB management)
via the USART communication, you can command the VNC1L to open a directory, open file, read it's content, or even write data to a file, close a file, and so.
(also you can check file sizes, read directories, and many other commands that you can read in the vnc1l firmware manual...)
the VDFC firmware allows to do the same file commands in any of the two pendrives, and adds a new command to "copy file from A to B", or even "copy all from A to a new directory in B" like a backup (read the manual as there are a few limitations)
the VF2F2 executes this last command with a single push button!!! what a neat module!
if you need further control of what to copy or not, you will need an extra microcontroller (and i suggest the
VDIP2 which have the vinculum and two uSB ports, you will need to download the VDFC firmware into it, and communicate with an AVR)
just for your information, there is a new generation of vinculum microcontroller, the VNC2, which claims that YOU can program into it (not only default functionalities but program it with your code (must download the compiler for the VNC2)!!!) it could be another option, but i don't have one of it so i can't be of much help in this VNC2.