The USG is a firewall for your USB ports, protecting your computer from BadUSB.
It connects between your computer and an untrusted USB device, isolating the badness with an internal hardware firewall.
The USG isolates BadUSB devices from your computer, while still passing through the data you need. The USG's firmware is fully open and auditable, so you can trust it. And when you use a USG, you no longer have to trust the opaque firmware of dubious origin running on every USB device you own.
You can protect yourself from BadUSB by using virtualised operating systems such as Qubes. But the USG is the only plug-and-play BadUSB protection that does not require you to switch operating systems. It can even protect your legacy and embedded systems running out-of-date software.