The owner of this devices uses it and he says it makes an audible improvement. You are saying he is wrong?
To be clear, I heard an audible improvement to the sound stage of my speaker system when using one AC iPurifier plugged into my power strip between my subwoofer (Rythmik Audio F12G, which may or may not have a SMPS) and my power amp (Schiit Vidar, linear power supply). I think I was using a Schiit SYS (passive, i.e. unpowered) as the preamp when I first tried that, with an iFi nano iDSD as the DAC, i.e. powered by USB from my laptop, which was plugged into a separate power strip. That improvement was noticeable and welcome, but it also took some back and forths to detect it.
That is normal when you don't know what to look for - if someone removed something small from your apartment, you might never notice. If they told you they removed something, it might still take you a day to figure out what. If they told you what they removed, you could usually confirm it within seconds.
New to power conditioners, I didn't really know what to look for, other than (less) noise, despite not having noticed any directly audible noise before. An improvement in sound stage I did not expect. By which I mean that instruments and voices had a more clearly defined origin in space, rather than basically just having three rough positions like left, right and center.
Adding two more seemed to have improved on that a teeny little bit more, but I very well may have imagined that.
Similarly, trying the iPurifiers with my headphone setup at work (Yggdrasil, then Jotunheim, now Gustard H20, Ether C Flow), I felt like maaaybe the sound had a little bit more... something to it, but it was extremely subtle at best. It certainly didn't make anything worse, while supposedly providing some surge protection, too (probably the claim I'm most skeptical about, since it's a plug-in device). I kept using them, for peace of mind. Another thing about power issues is that they fluctuate, depending on what other people are doing that might mess with your power, so even if it didn't make a difference in that moment, maybe it has prevented me from reduced enjoyment of my music at other points - who knows.
Recently I had an Audioquest Niagara 1000 on loan to review. After a lot of back and forth, I concluded that I can't hear a difference between it, the iPurifiers, or plugging DAC + headamp directly into the wall.
However, in my speaker system, very different story! I really liked how the music sounded with the Niagara 1000, which before I was only able to say about the subwoofer's contributions. Even better sound stage, but beyond that, a musical, engaging sound that is hard to deconstruct into particular elements.
So did it clean up my power even better? Maybe, but my suspicion is that it's the high current outlet that allowed the power amp closer to what it's capable of.
Will it do the same in your system? No clue at all. Too many factors involved, and too little insight on my end into the technical details.
Just to clarify the extent to which I currently belive in this stuff. I am not surprised the iPurifier didn't make a measurable difference, but it was still a worthwhile thing to test.