I too purchased one of these mats and tried it in my Uber Clocked Rega Saturn and also a Marantz SA-7 and Ayre-CD-5-XE ..... both myself and others did in fact observe what has been referred to in the above post as 'removal of some HF artifacts'...
However and more to the point, not only were some of the HF artifacts removed, but there is actually a wholesale removal of HF information resulting in what some have observed as more bass, which I believe to be in fact a result of our auditory perception curve when the entire frequency balance is tilted !!
Ultimately we observed LESS ambient information, which is quite apparent and not what I would call beneficial either... but to each their own, it certainly makes discs sound different and in the case of really poorly mastered, harsh sounding cd's it could be an asset.
Yet, I find applying a black Sharpie to the edge of such CD's & the application of Xtreme Av, Liquid Resolution on the surface is far more beneficial in ALL regards and actually have found the above to positively benefit ALL discs (although interestingly, some discs are significantly improved whilst others are more subtly improved), resulting in wholesale improvements to the entire frequency spectrum & definition with reduced granularity inherent to the relatively low res. 44.1 medium....
Unlike the Millenium Mat I have not observed any detrimental effects from the above applications, which can also easily be removed should one desire !
BTW: I also used the Boston Audio CD Mat which is a solid graphite compound, it too had essentially the same effect as the Millenium Mat, but far moreso, with a much stronger 'tilt' in perceived response as I refer above.
PS: FWIW-None of the transports suffered from any loading or operating issues whilst using the above mats