I'm sold on the concept. The execution is something I can't comment on from personal experience, but as far as the science goes, it seems solid to me. My understanding is that it's not only mitigating frequencies and that's the whole story. When you remove the ability to hear a frequency, you also remove it from what you want to hear. What it's doing is filtering the noise by changing the shape of your ear canal at the input end. From what I'm looking at in the cutaway diagram it's more like it's extending your ear canal and doing it's job before the sound gets to your actual ear canal. This is why it gives everyone the same result so they hear the same thing. The reviews and testimonials of top producers (like for U2, Brian Eno, Amy Winehouse for example) rave about the detail they reveal. It's their ability to remove the amount of information natural distortion covers up that makes the difference. A huge part of mixing is trying to clear away the noise and make a spacious mix with a lot of detail. Frequencies are only part of it. Reflections and ambient sound add noise, which is why we use environmental sound treatment. Honestly, bass traps work not too differently. They alter the shape of the space and absorb some of the uneven, slow-traveling low end sound waves by "trapping" them to reduce peaks and nulls in the mix caused by bouncing around too much at a different speed than mid- and upper frequency ranges. We use tons of plug-ins for this, but I wonder how many we would use if we didn't hear that noise in the first place. EQ and compression would be much more accurate, as would the relationship between tracks. There's also a headphone version that is shaped differently at the end where sound comes in to accommodate the direct, horizontal input. Headphone acoustics are not something I know a lot about.
I don't know... I don't think it's as simple as people are making it out to be.