I received my red APM Achromat from Funk Firm; it is flat. The differences are subtle, but it does improve clarity in the mids and highs. Bass notes are rendered with a bit more texture. One downside is that in order to get the VTA correct with a 180gm LP with my Quintet Black S the tonearm height just makes it when maxed out. I might be able to obtain a bit more flexibility with a headshell other than the Technics. It isn't an issue with the VM760SLC on A-T headshell.
I'll run the Achromat for a while before experimenting with a different mat.