TT mats

handyman,

I too, have an older VPI TT with a heavy metal platter.  I am using the GEM Dandy R.C.C. (Rubber Cork Compound) Turntable Mat.  Designed and sold by George Merrill.  BTW "GEM" are Mr. Merrill's initials.  He sells many well designed analog products and of course his own TT's.
Link to the RCC:  http://hifigem.com/rcc-record-mat.html  This mat is constructed of 2 different types of rubber with differing energy absorption characteristics and cork to aid in the transmission of energy into the mat.
A brief review link: https://www.dagogo.com/practically-priced-tools-for-the-lp-lover/2/
In addition, no discussion of energy absorption/control would be complete without addressing the myriad methods of record clamping.  I again will offer the following link that Mr. Merrill addresses: http://hifigem.com/record-weights-and-clamps.html
I am not familiar with the previously referenced Isodamp SD125 mat.
My RCC mat performs with aplomb at $60.  Spend your additional funds on proper record weights/clamps!
Good Luck

I use a custom made (as in I asked the guy to reduce the diameter) acrylic mat topped by a  Teac Washi  https://www.musicdirect.com/accessories/TEAC-Washi-Turntable-Mat
on my Oracle Alex III with an aluminum alloy platter.
I tried the Acrylic because that's what Oracle has switched to. It proved to sound somewhat cleaner than the Groove Isolator that I was using. Still, I didn't have the nerve to clamp mt vinyl down on such an unforgiving surface. Hence the Washi. 
These days I remove the Washi when playing 180 g LPs and clamp ever so lightly. This compensates for VTA (I tell myself ;^).

Anyway, it sounds very realistic and 'present' to me.

Combak Harmonix tu800 ex. It's not the i(improved) version. It came with my table along with the turntable weight. I think it's a VPI. Has two rubber bands on it. I took those off a couple days ago. I did notice a little more livelyness for lack of a better way to put it. I have been wondering about the mat and trying something else. A 10" record sounds like a fun and inexpensive experiment. 

Herbie’s Way Excellent Turntable mat!!!

http://herbiesaudiolab.net/ttmat.htm

Don't spend $400 on a mat.  Get the Herbie and put the rest towards a Stillpoints record weight.  Now that takes out the micro-resonances!

I use a FunkFirm Achromat 5mm in combination with a flexible, 1mm thick material I happened across, no weight/clamp..perfect!!!

Relegated my Stillpoints LP-1 to the top casing of my phono-stage.