I had a Nordost QX4 and QB8 in my system for around 8 years. I could always tell when it was on or off and had condicted a few blind tests with friends and family over the years. It added a certain vibrancy and texture to the music while maintaining a relaxed quality if that makes sense. Some could hear it most couldn’t, I was the only one that cared. For me, in my home (good power new(er) construction, cables and conditioning is about a 5 percent gain, sometimes at a $5,000 cost. Small gains for me and ultimately not worth it. To each his own. I think it big money systems with room treatments and great setup it can make a bigger impact than my $15k or so cost with good setup.