Recently I had the opportunity to compare the two mats - Harminixa TU- 800EXi (improved - 3 mm thick ) and Boston Audio Mat 2 (5 mm thick).
Tests were carried out on a mass loader turntable, where the platte surface is a copper plate and covered with a thin layer of lacquer, so the mat is necessary in the first place for reasons of safety, followed by sonic reasons.
Both mats are generally very good, but at the same time the mat both differ from each other considerably. Sonically are two completely different worlds.
Harmonix mat is made of something that looks like pressed paper layers.
Sonically gives a nicer, a more human vocal, more fine treble, better impression of air and high frequency stretch.
Harmonix mat at the same time gives a more rounded sound and reception as a whole resembles the vacuum tubes.
With this mat defects - weakens the edges of the attack, the attack is not as fast and dynamic like with Boston mat.
Listened immediately after the Boston Audio sound gives the impression of slightly coloured sound. At a midrange the sound become a little haotic, compared to the Boston Audio.
Boston Audio mat is made of block of graphite.
Sonicaly it goes in the direction of the sound more dry, precise and analytical. Overall it sounds more like a solid state gear. This gives a faster response and better edges.
There is no such liquidity, analog sound like with Harmonix, but the overall sound brings more excitement. Very organizes sound - everything is in its place stated in very clear and precise way. With flaws - slightly reduces the maximum frequency and the aura of reverb that comes in direct comparison to Harmonix.
In summary, each of these mats is quite different, and each will appeal to different listener.
I will be trying to look further to find a solution that combines the best features of both of these mats .