I spoke to the guy that does the ebay custom ones that you linked to traversleigh. The ones you have 96vscommodore are ones that go over the top. correct? The more expensive ones that come from the US are complete replacement Clusters. They have their own independant lighting systems and do not use the stock LED's or Stock cluster. I believe you have to wire them in yourself but if you can wire a CD player into your car you should be able to wire the new cluster in. Im not sure if the Speedo's have to be re-synced or if they use an existant component. If they do have to be resynced you are better off changing your cluster to possibly a Level 3 (if you own a Level 1 or 2 cluster) as the Level3's look heaps better.
With the expensive Clusters you can also get custom lighting done or custom graphics. Its worth the money to pay the extra and get the new custom clusters i reckon. Sorry 96vscommodore, i dont like the look of the cover-over's. i think they sorta look fake and plastic and they also do not show the light correctly as they still use your exisiting LED's i beleive. *this is my understanding of it anyway*
I have spoken with the guy from the US over MSN and he seems to know what he is doing. How-ever he has only done one custom BT1 cluster and has sold about 6 of the Climate Control Panel's. But he has done a range of other cars including RX6's i believe. Anyway thats my 2 bob's worth.