I had my Cayman S done with the 3M product by Pfaff when I bought the car. They charged less than half the numbers quoted above, but there were a couple of air bubbles. They redid the installation to my satisfaction. I assume they are using outside contractors, but they do it at the Pfaff shop.
There is slight amount of colour change between the protected and unprotected areas, my car is Lapis Blue.
I am glad I did it, there are some marks on the film from stones, and those probably would have caused a lot more paint damage.