I did buy the Blue Circle PLC Thingee (I wish they would change the model name because it is really) stupid. Fortunately, I have no complaints. I does seem to eliminate RFI noise and broadcast interference, but I don't know how one would measure that, except that I live in new apartment complex in downtown Los Angeles which probably has appliance going on and off night and day.
However, I did notice some compression of the sound and a less tighter bass.. I have been advised by several people that any PLC may remove RFI, but also compress the signal.
I would use it on the my LG TV and cable box if I could get it closer to them but why bother to see the Bachelor or The Voice with better definition and color. My only hope is the BC PLC could make some cable shows and movies sharper and brighter which I am told is strongly related to the software used by the cable company to save money.