As it happens, given events of the past three days, I can address your request, Ken.
I will qualify all of my comments because I believe that the effect of any of these additions will be dependent on your specific setup (table/arm/cartridge). I speak from the experience of using these with Spacedeck/OL Illustrious/Shelter MkII.
First, I have had occasion to hear the Spacedeck with and without the "Heavyweight". My analogy is that the Spacedeck, in original configuration, is like Ali while, with the "Heavyweight", it is like Liston. Hopefully, ya'll are old enough to appreciate the comparison. Fer dem dat ain't, I found the "HW" stunted the quick, fluid, and rich sound to which I had become accustomed with the original platter, etc. IMHO, a waste of good money that one could spend much more effectively elsewhere.
I bought a Mat1 after reading carefully the website and being impressed with the detail and "philosophy" there provided. I was less than impressed with the "fit and finish" of the mat I received, particularly in light of the website's emphasis on tolerances and quality control. Mine had some grooving (a bit strong to call it gouging) on the underside. The upper side showed clear signs of overlapping finish coat application. As a former apprentice to my master craftsman grandfather, I am more than picky in that regard. But, it would not have left his shop without being classified as a second with an appropriate price reduction. I have heard from others that they have, in fact, obtained "seconds" of these mats for a substantial discount. I paid full price. Unless I received a second by mistake, I'd not wish to view other seconds. I am in contact with the "maker" but have as yet failed to achieve resolution.
To be fair, the PERFORMANCE of the Mat1 belies its appearance. It obliterates the original foam mat and easily bests the Ringmat I had laying around. I realized a better level of detail AND dynamics but I did not lose "PRAT" (everyone's definition is different) like I did with the Ringmat.
Three days ago a friend who owes me a favor brought over the Mystic Mat he purchased. I refused to pay the dough for the Mystic Mat for a variety of reasons that I will not detail. In comparison, I like the Mystic Mat better than the Mat1. The Mystic Mat provided an improvement that is hard for me to describe. For one, I found that it smoothed out the ever so slight sharpness of attack that I have heard with some other mats (and, yes, I allowed for VTA changes). The sound when using the Mystic was rather suspended in air, for lack of a better term, Kinda like when you hear something through a very good tube system, as opposed to a so-so tube system. If they weren't so damn expensive and I could overcome my personal issues with the distributor, I'd probably buy one. Oh yeah, the MM is designed to be used with a record clamp. It comes with the Michell basic clamp. There is a further improvement on the butt end of things when using the clamp, much to my amazement.
Anyway, I've blathered on too long and said little. Try different mats and keep the one that sounds best in your rig.
David