In the product description, one of the features it boasts is "Brief Mode", wherein it only copies those sectors that contain data. My question is, how does it know which sectors contain data? Is it file-system aware (it does mention that it supports most major file-systems)? If so, will it be able to duplicate USB drives that are encrypted using full volume encryption (in "brief mode")?
It is very likely that the particular device in question is using filesystem metadata to figure out which sectors are in use by the filesystem.