I bought this to enable me to plug an XLR condenser Microphone into my Macbook. The device functioned 'out of the box' (e.g. no driver installation) which was great. To get vaguely decent volume levels required the on-device gain and OS-X gain to be set to 'Max'.
During an audio recording, significant noise (hum) is heard in the sound signal, consistent with a switch-mode PSU in the device (continues when mic is unplugged, and with 48V switched on / off).
USB interface on the back is fragile, and cable is not of high quality, the knob on the device is small and difficult to adjust, and doesn't travel fully around.
I have returned for a Focusrite Solo (£80) which is a desktop box, and would suggest you consider the Shure X2u if you really need the 'inline' form factor (but haven't tried either).