Oh, interesting! I hadn't seen this product before. I see they also have this, which would allow you to connect it to a (probably more precise) multimeter: https://www.adafruit.com/products/1456
That usb tester you can also get in this config, I have this in an earlier version:
https://www.tindie.c...ster-20-bundle/
I switched to this later: http://www.ebay.com/itm/171606912751which works very fine, but I have the backplate for that usb-tester so I can connect it to an agilent 34461 multimeter for better precision (and logging)