I have a Nottingham Analogue Studios Spacedeck and would like to offer my experience with the two mats I have tried. First, the table comes with a fairly thick, 1/8" dense foam mat that Tom Fletcher, the designer, intended to be used as "a dust cover" for the most part from what I have read. The sound was not bad at all, but a little dull and lacking the "sparkle" I was after.
The other mat I have tried is a cork Music Hall mat with the small "pods" around the thing and a separate cork disc that is place over the spindle to adjust the record height at the label, presumably to cause the record to be supported at the same elevation as the pods but for me that was not the case. The problem is that when I use my ADC Pro Grip clamp, I can see how the record flexes with the outer edges elevating.....not good. First thing I noticed was trouble with getting the stylus to catch the lead-in groove, presumably because of the flexing thing raising that outer edge a bit. The sound was a bit livelier than with the foam mat, but I could not tolerate the flexing with the clamp on.
So, one day I just removed both mats and played a record placed directly on the platter, which is metal, impeccably smooth and lacking any orifices (holes) in it. I was surprised at how nice it sounded and have been using it that way ever since. The clamp now just secures the record to the surface of the platter without the flexing and seems ideal. Of course, I had to fiddle with my arm a bit to get correct VTA given the different heights of the record with and without mats and double checked the VTF each time as I was experimenting but this is what I have settled on currently. Not sure this would work as well with other tables that have a rougher surface on the platter.....