I did a lot of researching on the topic and most people agreed with the above...they preferred the felt mat on the LP12. I just picked up one of the Extreme Phono None Felt donut mats for my LP12 and I like it quite a bit. It really does everything that Extreme Phono claims it does. It is more detailed than the felt mat, but musical, and it doesn't change the sound for the worse (like many claim the Ringmat does on an LP12). It's a different listening experience from the felt mat, but still the same thickness, so no real need for adjustments.
Some people have said that the None Felt mats are made from a static free shelf liner available online from other sources. I did check into that and it might be true...the products do look similar. The shelf liner was $13 (plus shipping) and the already cut donut mat was $28. I don't see that as being the most ridiculous mark-up in the world, and Extreme Phono did seek out the best mat for the use...I didn't have a problem paying them $28 for their service.
Other people have also said that the mat leaves a residue on their LPs when they leave them on their TT for hours or days at a time. I have not seen any residue with normal use, but it may very well be true. It is some sort of a rubber-like compound and, like sorbothane, it may "leak" chemicals. I highly recommend checking them out, but I also highly recommend not leaving your LPs sitting on it for more time than necessary.