I have the Harmonix TU-812 as well. On some music, it sounded pretty good, much more airy and clean on high frequencies. But on others, it seems to be taking away some of the lower frequencies. It had similar effect as the DIY African Ebony, but just not as much on the bottom end.
The name of the eBay seller is hk-gadgets. He only lists in the UK eBay site. He also sells ebony feet, other audio stuff, and Chinese tea. I didn't see any record weight listed at the moment. You can e-mail him for more info. I have a suspension table, so I bought the smaller one. My friend bought the heavier one and says that the effect is better on his table with the heavier one.
FrankC