Nice find dominic. When looking the vendor site, i did notice the following for our Nexus 7's:
Galaxy Nexus, Google Nexus 7 (2012 Original & 2013 New) & Nexus 10; requires third-party software or device being rooted.
Not taking away from the device, but my interpretation is that the device works like a compact OTG cable. This requires Nexus media reader, Nexus media importer, or Root and Stickmount for the device to function on the Nexus 7. Notably, Root and Stickmount is the only option to write to the device from your Nexus 7 with OTG, that I have seen.
I look forward to you receiving the device and reporting on any OTG variation. The compact design is interesting and would eliminate me carrying an OTG cable, a Usb card reader, and a Micro-Usb card adapter. I have enough stuff to carry as it is and $15 is a small price to pay to eliminate baggage.