What I like about the full version is the pitch and tempo controls. It's easy to change either one while the song is playing. It also some FX (delay, compressor, rev) and some noise canceling presets (hiss, hum, A/C, wind).
I've found it to be good at zeroing in on whatever you want to remove but, unless the noise is pretty isolated, you also remove something you'd rather keep. That isn't unique to R-Mix, though. $20 is a good deal. The disk I got from Sweetwater didn't work, so they got Roland to send me a disk that did work.