The iTwin USB stick is the literal version of the web-based file hosting service Dropbox
How the iTwin USB stick works is that the two halves must be connected together first in order to create a password; that way, data transfers are more secure. Users can then leave one half plugged in at home and bring the other half anywhere and access the same files. As long as both computers are on, files can be edited and transfered anywhere and any time.
While Dropbox is extremely convenient, the iTwin is much safer when it comes to data sharing since you're not doing it online. Gadgets such as the iTwin are often designed for convenience, but now it appears security is becoming an important factor as well. It's always been risky sharing files on the web, but perhaps that problem may soon be resolved.