CD Mats -- do they work? Are they dangerous?

I'm not sure they're all voodoo. There are several companies - Esoteric, Electrocompaniet and maybe others, who feel that clamping the full surface of the disc is a better way to go than just in the center. So, from a mechanical standpoint, the CD mat may accomplish that goal to some degree. I've tried them, but I haven't really spent any time doing A/Bs. I don't think they're "dangerous" in most players, but some players, such as the Esoteric X-05, specifically tells you not to use it, perhaps due to its full-clamping transport. I would also hesitate to use it on some "puck" players, such as Naim, where the extra layer of material may weaken the magnetic bond, causing the puck to fly off and into the machine during play.

123,

Have you tried that carbon fiber one?

No, I haven't tried the carbon one.

123.

I have the Millennium CF and it is worth the price of admission.

I have to agree with Cruz123, I use the Marigo Signiture Refrence with my ARC and yes, it does make a difference, in fact I don't listen to a disc without it. I've had zero problems in use with it, and yes there is not a huge difference but enough of a difference that I'm satisfied that I spent the money for the improvements it provides for me. As with any tweak it is an subjective judgement, if you can get it on a trial basis that would be a way to go for you, also contact your manufacturer and see what tech has to say about it's use as well.