I prefer copper because it adds support to the shower mixer. If you can
solder one joint, you can solder 6-8 allright..and right angle bends are
all in the days work. Then with plastic supplementary bonding raises its
ugly head...and as you have pointed out how to attach it to the shower
unit..

Supplementary bonding is easier with plastic. It doesn't need any.

However, I still agree that showers are best done in copper, purely because
of mechanical strength.

Christian.