Graham,
I never cared for having the record on the Acrylic and clamped. It always sounded "edgy" like that. I did my own DIY mat and liked it (smooth, natural, relaxed), but could not use a clamp with it because it would sound too damped.
The Herbies mat does a much better job than my DIY mat and also allows me to use the clamp without the negative effects of overdamping. I'm getting better low level detail and a relaxed natural sound. It sounds just right.
It has just the right amount of damping, so in my book, it's a keeper.
- Tim