Find yourself a good mercedes specilist and stick with them, they may charge a little more but the job is done properly.
I suppose fitting the sheilds properly will mean that they use more cable ties, classy.
Where in the country are you?
Stevenage/Cambridge. The Halfords branch in question here is Welwyn Garden City.
The problem is not so much that they used cable ties. The problem is that they used those ties to join one shield to another - with no connection at all to the bodywork.
When I complained they said that the reason they used ties is because there were ties there when the car came in. I do not know whether it is true or not. However if at least they used ties to attach these covers not just to each other but to the body of the car as well I am quite sure this would not have happened.