THe aluminium is certainly metal. Its a metal face on a plastic base.
The only trim that is entirely made of plastic is Titanium shadow.
I went with CF in the end. I had aluminium in my old E46 M3, and although it looked good, I wanted a change. The aluminium has also being played out to death in the rest of the model range as well. One other thing, I found aluminium is really easy to scratch so be careful if you have rings, watch straps, or anything that could scratch the metal finish easily.