I just picked up this DAC last week and have been loving it! I would tell you what I upgraded from, but I prefer not be laughed at, haha.
I will say that when it arrived, I couldn't get the USB portion to function. It bummed me out because that is one of the reasons I purchased this unit. I simply could NOT get the DAC to show up on my Retina Display Macbook w/ Mountain Lion. I troubleshot with Kingwa (who was great to deal with and responded very quickly), and after trying several things, we figured out that it was an issue with the USB 3.0 ports. When using the USB 2.0 port of my keyboard, it worked perfectly. With the built-in 3.0 ports, no dice. Kingwa is working with their vendor for updated firmware support.
Anyway, just posting this in case some others experience problems with USB 3.0 ports on their Macs before the firmware issues are resolved. =)