Tim - the one concern I have over the all metal gear knobs, is that in the sun they will get very hot.
I have an all metal, or mostly metal one in the golf, and it gets red hot during the summer, so much so that I blast the aircon onto it for the first 10 minutes of th drive home after it being parked up at work all day.
I take it from your previous post you have had this issue in the Z with this knob fitted?