I did an initial comparison of these CD mats.
The Super Black Hole (SBH) is a small carbon fiber mat, only a couple inches in diameter, with a sticky silicone layer. It does NOT cover the entire CD, an important aspect of its design. It costs about $32.
The Millennium is a carbon fiber mat exactly the same size as a CD. It has no sticky layer, but a very smooth surface. It costs about $100.
How and why do mats help playback? I'm not sure, perhaps multiple theories apply. Vibration control, electrical field control, others? No doubt the effect is relative to the model of CD player and its relative faults and merits.
My CD player is the Naim CD5X plus FlatCap external power supply, about $3900 in 2006. Loading mechanism is magnetic puck. Naim claims vibration considerations went into the puck design, but it's not as advanced as their higher models.
I used the K1000 headphone.
Amp was the Audio Note P2SE, a class A amp based on the 6L6 output tube.
I've been using the Super Black Hole for many listening hours now, and gotten used to that sound. So the first thing I did was grab Sheffield Lab's Dave Grusin album, replace the SBH with the Millennium, and just see what struck me first.
The sound was impressive at first. But when the drums and bass got loud, they seemed very punchy, to an exaggerated degree.
I put the SBH back and listened to the same track. Right away I noticed the top end "air," delicate highs and subtle dynamic changes in the cymbals and bells. The Millennium was killing those things!
With the SBH, when the drums got loud, they seemed natural---plenty punchy and tight (thanks to the good work of Sheffield!) but completely natural. It seems the Millennium was in fact exaggerating the punch.
Next I listened to a piano recording: James Boyk playing Prokofiev's sixth sonata. On this recording are dynamics ranging from pppp to ffff. It's the most natural presentation of piano attack I've ever heard.
Again I compared the Millennium and the SBH. Again I noticed the Millennium seemed to exaggerate the attack. In the ffff sections, Boyk's playing sounded raucous, not a flattering effect in this piece. The same section with the SBH was powerful, and not out-of-control. There is a quiet section in this sonata, early in the first movement, which I love: a sudden peacefulness emerging from the early storm---at least that's how it sounds with the SBH. With the Millennium, the piano attacks were too distinct.. the legato (smooth) effect was ruined.
At this point, I conclude the Millennium would appeal to people who like "punch" and perhaps have a system that is tuned on the "loose" side to start with.
But it is no competitor to the SBH, in my system. The SBH improves everything without any downside (I've discovered yet). At $32 it must be the most extreme ROI of any tweak I've tried.