I used Zen front and back. I tried exceed too, use hard front, and soft or medium back, and only tyre water at back. However, zen combination is much bette.
Yes it does. Obviously not for big crashes. The screws are positioned at roll over touch points, and if the car rolls, because the screws stick out for 1-2mm, the body is slightly kept from the ground, so reduce the cutting into the lexan plastic by the ground. It's just a small but extra protection.
(and I guess it looks cool on top of window too.... )