I have the Cinepro 20 Line Balancer in a two-channel stereo system, and it was one of my best additions. I can be set to play an LP at normal listening level and not be able to tell, with my ear against a speaker, that the system is on.
The idea behind them is brilliantly simple, not even all that original, since it's how power comes into our houses from the poles outside. But the implementation matters too, and transformer quality is important, and they do that well.