There was a dyno done on a similar design of intake and it gained like 8HP over a regular aftermarket short ram intake. The numbers that the Weapon R states are exaggerated. The true cold air extension will perform better. Just think about it this way:
The reason that you buy an aftermarket intake is to increase airflow. Which any intake does simply by replacing the airbox with a cone filter. The filter is still in the engine bay though - and sucks in air that is heated by the engine. Colder air means more HP, so there are designs created that allow the intake to take in cooler air. Weapon R put their cone filter inside a heat shield box to keep some of the engine heat from entering the engine. They also put an extension tube that feeds outside air into the box. So it takes a little bit of cold air from outside and reduces the temperature of the heat shield box kind of like an air conditioner. This is much better than a regular short ram setup because you are reducing the air temperature, but in essence the intake is still in the engine bay. The air is cooler, but it is still being heated by the engine. The extension true cold air intake just puts the whole filter outside and only sucks in outside air. Much colder air = More HP! Oh, and the costing twice as much part... There was a very competitive market for this design a little while ago. That is why the price is so cheap. I got mine when it first came out and paid $149 for just the extension tubes. Keep in mind that I paid an additional $110 for my short ram setup. So this intake cost me $259 total... And it's worth every penny!
For the pre-cats... By gutting the pre-cats, you would be freeing up airflow. It's kind of an inexpensive version of headers. It isn't as good as getting headers, but it is free and is much better than the stock setup. The pre-cats have a honeycomb type material inside them that the exhaust flows through to reduce emissions. You would be removing the honeycomb material to let the air travel through the pipes without restriction.