Have used a Ford Escort with one. There are no visible filaments,the screen is exactly the same clear shade as one without the heating elements. They are fabulous. In icy misty conditions they clear the windscreen remarkably quickly.
Mind you, given the Micky Mouse electronics on the MINI, you will probably get 2,000 volts through your backside each time you turn it on. That, or cooked gonads from the heated seat.....
I had one on a 1991 Lincoln. Greatest device for de-frosting, de-icing I can think of. Start the car, push the button and turn the wipers on 2 minutes later...presto, clean. I live in snow and ice for 3 months a year. I want that option on the MINI and hope it lives up to past experience.
Buttercup, my Fiesta XR2i based Quantum H4i ( see my Avatar ) has a heated windscreen, and it works well. You can see the elements if you look closely, but they are not noticed when driving, and looking 'through' the screen.