Per the included html documentation:
The signal source may be a sound input (preferred) or a data slicer (provided for compatibility).
You'll have to test the data slicer yourself to see if it works for you.
As far as the advantage, the biggest one for me is that I can use the MIC input rather than the serial port. Most computers now a days have only one serial port, and in some cases
none! I only have one port which is used to control a separate radio for voice listening.
The author of UniTrunker states that the sound input is preferred. I'd imaging it has something to do with the internal coding structure, but he'll have to elaborate on that himself.