Which cabins have a metal fronted balcony?
On Queen Elizabeth and Queen Victoria - BF grades 4001 through to 4042 (excluding inside cabins) have metal fronted balconies.
This example is taken from 4042, Queen Victoria
Queen Mary 2 BU, BV, BY & BZ grades have sheltered enclosed balconies.
The following question may also be of interest to you: Which balconies are shaded / partly sheltered and what do they look like?