You didn't add the shipping cost of the USA headers as well. Since they have delayed the release many times because of rejecting the header samples that they received, I sure do hope that their headers are top notch. From the early pictures of the headers, it looks like racing headers (like the Toda), so the gains should already be better than the off the shelf brands like Comptech. There is nothing wrong with custom designing your own headers. Just because there are branded headers out there, doesn't mean that they are the best.
The thing is, the sum of all the best parts doesn't usually equate to the best result, at least with regards to car tuning. Instead of going for the best parts in the market, the better way would be to go for parts that complement each other. That is not easy to do unless you design your own parts to work with each other. :)