If you are just planning on testing usb devices, just get this guy for $2 http://www.ebay.com/itm/USB-Power-Amp-Meter-Tester-Charging-Monitor-Voltage-Current-Multimeter-MA-/322162304963?hash=item4b025ea7c3:g:k1MAAOSwOVpXaSV2
works just as well as the much much more expensive testers I have.