IC for Monitoring USB
Here is how I would monitor USB traffic, slightly off topic as it is a software only solution rather than a hardware solution:

@m.Alin kindly pointed out that Wireshark supports USB on Windows too, so basically the answer is: Use Wireshark for snooping USB traffic.



My previous answer is still valuable as an alternative:


On Linux: just use Wireshark, you can snoop USB traffic out of the box;
On Windows: 

Install Linux as host OS on a PC;
Install Wireshark, Virtualbox and Oracle VM VirtualBox Extension Pack. Both Wireshark and Vritualbox are available from standard repositories on all mainstream Linux distributions. The Extention pack is only available from the Oracle website.
Install Windows as a guest OS in VirtualBox
Configure VirtualBox USB Device filters to feed through the USB device that you want monitored to the Windows guest VM; 
Use the USB device as intended from the guest OS;
Monitor the USB traffic using Wireshark from the Linux host.