I have an Acoustic Signature Samba TT w/a modified Rega 300 and a Denon DL-304 cartridge. I replaced the stock felt mat with an Oracle groove isolator and it was a huge improvement.
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I have a Technics SL1210, and I too stumbled onto an Oracle Groove Isolator. Got a used one for $10. This is an excellent match for an aluminum platter because it's sorbothane, but not sorbothane gel. It's heavy and dampens aluminum's inherent ring really well, but it's not sticky like gel and doesn't suck the life out of the record.
I added a layer of polypropylene mesh on top (cut from a roll of drawer/shelf liner) to give the presentation a little more liveliness and sharper leading transients. I think aluminum platters need a mat that does two or three things well--kill platter ring, isolate the LP/cart from noise, and control LP resonances. So don't be surprised if a 2- or 3-layer approach works best.
But the Groove Isolator is a great place to start.