[DonC]

I purchased the Invincashield pre-cut product for my ERA when I got the car in 04. At that time Invincashield had only one or two pre-cut Cobra packages although I understand they have more now.
Had the installation done by one of their recommended installers and watched the guy put it on. Took several hours but looked good when he finished.
Fast forward 6 driving seasons and 40,000 miles. The product is still holding up very well. There have been one or two places where larger stones have penetrated the product but over all it has done an outstanding job. A number of club members have far fewer miles on their cars and you can really see the damage.
Very pleased with the product's performance. If I'm careful about cleaning the edges of the material where it meets the paint you can't even see it from 10 feet away.
A new alternative that I've just become aware of is a product that's applied by your local paint/body shop. Supposed to be just like the 3M product but applied like paint. One of our club members just got an RCR GT40 and had the entire front end shot and you can't even tell it's on the car. Don't have any durability information yet but if it holds up it may be the real way to go in the future.
Other local people I've talked to have had the 3M product applied by shops recommended by their local Porche dealers. The apparently use it quite often on the front of the Porches.
DonC