Ok I have a question just what is the Iris and why would it be important to have a brass over Nylon?? I have the Portuguese with the nylon Iris, but I don't know what that is. I has served me well so far.
In theory the brass would last longer than the nylon over time, the frame on the Italian model is taller and sturdier but like you have said the Portuguese model does a great job.
The iris is the part that compresses the cork for insertion into the bottle. The brass iris will last longer, but I can get a replacement iris for the nylon model. To me, the best reason for the brass iris model is that is handles the 375ml bottles much better than the nylon iris model. The 375's are shorter and some of them are too short for the nylon corker.