You could use either or even Fatmat, that is what I used on my C5, price is around the same.
Installed when I first put my Corsa Indy Pacecar exhuast on the car and to also kill road noise.
Since then with the engine mods and the Extreme exhaust its become loud again but thats ok
have a new stereo system going in the spring.
I used a heat gun and hair dryer to help form and mold the material over the contoured surfaces.
Also purchase a small wallpaper roller to flatten the material out and get a good bond.
I cleaned the back area and vacuum then with some water and towels and allowed to dry,
try to get any stones or small debris off the surface or you get bumps all over the place.
The doors where very easy after the panel is removed, I just double lined the door cover on the
inside, you can also line the inside of the door (backside of outer door) if you wish.
Very simple and straight forward, easier to work with the material in warmer temperatures.
Here are some pictures.
C5 bare:
C5 Fatmat 2 layers installed:
C5 Foam installed:
C5 Door Panels: