New Funk Firm Achromat Warped

If its the 7mm APM you may be better off as I believe that has a glass substate that I'd expect to be flat. The lipped 5mm version I had for my 1200GR was flat and very good sounding IMO - so I think you'll enjoy the results with your GR.

The one I just received was the 5mm standard foamed acrylic mat. As you can see from the pic below its dish warped and contacts the platter only on the label area. I didn't try sticking it down with the Funk supplied adhesive dots as I want to retain the ability to swap mats - plus don't know if the dots would actually hold it down. I think its unreasonable for a rigid turntable mat at this price not be flat - that's a primary criteria in my book. I contacted my dealer and arranging a replacement.

https://www.dropbox.com/s/nlen08tuigrmg3w/20220407_111640_resized.jpg?dl=0

throw it in the dumpster.  ruined the bass on my turntable.  

mats are best used to damp the audible tonearm resonance that can color the midrange.  

the way to test this is to play bass beat music with vocals at higher volume to make the differences more obvious.  

compare bass impact, bass note definition and vocal midrange clarity. 

the achromat on my technics seemed to blur and cancel bass notes, reduce their sharpness and impact and fog the midrange.  

try another, there are clear winners out there for the latest technics tables. 

I eventually went with the Boston Mat on my SL 1200G.

the achromat on my technics seemed to blur and cancel bass notes, reduce their sharpness and impact and fog the midrange.

That was not my experience with the GR.

FWIW, I received my replacement Achromat and it's perfectly flat.

Sounds great on my Technics G. As with the GR the Achromat enhances midrange clarity, focus and separation of instruments/voices compared to the stock rubber mat - sounds really pop. So my impressions are completely opposite to @avanti1960. Some may prefer the more laid back sound of the rubber mat.