Gregm. I have tried all materials known to man (ask my wife how many shelves lurk in the basement), so can report on Perspex. The best thickness seems to be around 12mm. It is really too heavy in my opinion and not damped sufficiently in the lower treble. Therefore you get good bass weight, but slightly behind the beat, and a bit of accentuated presence. The accentuated presence gets obscene if you support the perspex with spikes, or if you use cones between component and shelf. In particular the BDR cones seem to really set off a mutual resonance with Perspex. I found Corian to be better (which is also an acrylic but much denser than Perspex) than Perspex, and really not bad. But neither approach the Neuance. If you use Corian or Perspex, I recommend using very thin hard rubber pads (3 or 4) between rack and shelf. And then use soft footers between shelf and component. This will tame the resonance I have referred to reasonably well and if the footers are Vibrapods the bass will speed up a bit.
The Neuance is not a perfect solution, but it is damn good. Being very light compared with what most people use for shelves, you will find the bass is much faster, but you may find it lightweight compared with what you are used to. I reckon the Neuance is just more accurate, and the bass weight when using heavier shelves comes from the energy stored by those shelves being dissipated slowly - causing a perceived slowing of the bass. What you prefer will depend on whether you prefer the bass weight or improved PRAT.
The other issue with Neuance shelves is that the heavier the component, the more you tend to get a bit of unwanted warmth creeping into the lower mids and upper bass. I reckon that Neuance is trying to make a shelf that tries to optimise the trade-offs between each of light/rigid/damped, but that when the component gets out of the expected weight range it starts to flex a bit. That is probably why they make an alpha (for light components) and a beta (for moderately heavy components), and I think Ken is still working on a shelf for very heavy components. So it is a good idea to get the right grade shelf for the weight of the component to avoid the only slight coloration I can detect with the Neuance.