+1 for the Eau4! Bought one initially for my OLED TV to see if it made any differences(s) and indeed it did. After about 10-12 days, better color saturation and darker blacks. What I dd not expect however, was the impact it had on my stereo system which is on a separate line but fairly close to my TV.
My system became quieter, especially in phono mode. I was so intrigued that I ordered a second one and plugged it into an outlet with my stereo and the noise floor was further lowered to a level that I can no longer detect any noise. Prior to inserting these devices, I could always detect a very slight hum in phono mode (behind my speakers) when I stopped playing a record. With my system off, the hum would disappear. Now, I can't hear any difference in the hum level when my system is on or off. Color me most impressed!
With the reduced noise levels, my stereo sounds more dynamic, has improved imaging and sounds a bit warmer since I am more aware (in a good way) of the tubes in my system.
The company offers a 30-day return policy, so you really don't have anything to lose, except for the time and effort it would take to actually audition the device...before passing judgement. I realize that for some, the later comes much easier.