From what I understood from the material found at Wireless File Transmitter WFT-E4 II A, this device is capable of connecting to an external USB hard drive.
But the site is not clear on what "connecting" means.
Does that mean that the photos will be saved "online" to the HDD while shooting or does that mean I can shoot saving to the CF and later sync to the HDD?
From what I understood, the device does the first option, but I'm interested in the second option. That would allow me to backup to a hard drive without the need for a netbook or a more specialized gadget (such as those devices that combine HDDs and card readers in a single device).
It does take a bit of digging through some of Canon's international sites, but to quote Canon Japan:
An external hard drive is recognized by the camera as "External Media," using the [Automatic switch media], [Record separately] or [Record to multiple] function. You can also designate an external storage media as the destination directory for the [Image copy] function.
This gives you both the options you'd proposed (as well as additionally supporting writing to multiple locations simultaneously)