Chip,
In case you're generalising and including Creative Carbon's Cossie stuff in your sweeping statement of excluding the stuff us Ford people buy from being the same F1 spec / quality, I would just like to point out Marcus's items are all made using the same processes as the F1 spec stuff (as in pre-preg vacuum formed in an autoclave) - he also does these . The only difference will be the number of layers (as a splitter or heat-shield doesn't need to support quite the amount of weight .