I've been doing music production for 25 years, working with tape, digital, you name it. 5 years ago, I focused my business almost exclusively on mastering.
I had just received a New Orleans Jazz Brass Band CD to master when this plug-in came out. Perfect timing! This plug-in was just the thing to smooth the rough edges of the brass section (800 Hz - 5 kHz range) without damaging the tonality. It is also useful for smoothing in the mix context - anything that has that biting, harsh, grainy edge that is so often the downside of digital, especially the prevelent cheap converters, microphones and pre-amps in project studios.
Many of my clients send me mixes that have an excess of digital harshness. Though I had developed ways to smooth out their mixes, the bx_refinement tool is a kind of 'One Stop Shop' for the job; better than any tape emulation, eq, multi-band compressor or other effects I have used for this purpose.
The bx_refinement is not just useful for mastering. If more of my clients used it in their mixes on the harshest tracks, it would make their mixes a lot better and my life a lot easier..
The presence effect is nice too. Just don't overdo the Saturation on tracks that already have a lot of character.