I now have three of these Siemens Nixdorf boards. One is missing the wrist rest. It was the cheapest but turned out to have the least yellowing. So, they do yellow. I paid too much and should have gotten one or two less. Oh well.
These are rubber domes but with carbon contact, not the standard membrane switch.
The construction has improved on the Cherry ErgoPlus with a different 'roofing' mechanism that avoids the weakness in the middle.
I expected to find some hints inside that these were actually made by Cherry. I found nothing, no clue whatsoever. Just some logo I don't know.
The 'pcb' is like nothing I've seen before. Regular circuits printed on a membrane. Controller, LEDs, everything is attached to the membrane.
The rubber domes have 'silicone rubber' printed on them.
The cable is detachable (phone jack type).
Switch feel: starts with the typical rubber dome tactile cycle until it makes contact. After that you have to push harder. That resistance stays about the same until the keycap bottoms out.
Now for the pics (anybody recognize the logo in the last pic?):
Someone needed an 'A'.