The RingMat is a great sounding mat on many tables and in many systems. like anything else, it is system dependent. They have a neutral and somewhat lively sound with excellent bass depth and definition. They work especially well on acrylic platters where a softer mat really sucks the life from the sound. They also work well on tables with glass platters where the set-up has a warm or neutral balance. They will not do a thing to dampen a platter.
In this case, the fellow wants a warmer, more lush sound and the aluminum platter on an AR needs some dense rubber to best deliver that. Having his table inside of a cabinet doesn't help with resonance control either.
Mats and cartridges as well as tubes and SS all seem to come and go as far as audiophile fashion has it ;-). What self respecting analog maniac would be caught without the most unusual and latest of platter coverings?! I think it's silly actually and although I have tried a lot of mats on my Rega tables, I still go back to the old felt mat that came along in the box. Boring perhaps, but very nice sounding. I also have a RingMat which I don't use since I have had the Regas and have found the felt to work best in my almost always neutrally balanced systems. However, I have made yet another change in terms of system balance and it is a bit on the warm side these days. Hmmm... I think I stuck that RingMat jacket in the Lp library right at the begining of the A's... ;-D.
-Bill