Since I owned an AirAid and have a custom CAI that I built myself, I thought I'd chime in. One advantage I have with my Flex is my Carriage Works Grille which allowed me to remove all the restrictive plastic stock grille backing. More air naturally gets to my radiator, and can directly get to the filter area. I have a 170 Deg T-stat installed, and it has a factory Traileer Tow package. Flex's also have larger radiators and don't have the overheating issues that seem to occur in 2010-2012 SHO's.
My custom CAI is a RotoFab "J" pipe that is similar to the pipe on the K & N in shape, but I added extra piping where it attaches to the stock system and reversed the bend, so my filter is farther into the fender area. I have used a couple different cone filters and have always covered them with a K & N filter cover (pre-filter). I also made a heat shield out of plastic that also works to route cool air from the grill and the opening above it towards the filter area. This is one of the issues I see with the K & N in that the shield is positioned on the wrong side of the front air inlet.


As for the AirAid, I bought it when they had a super deal +$50. rebate. I tested it for a couple days and found my engine temps ran several degrees hotter, and IAT temps didn't cool down nearly as fast as with my custom CAI. This I attribute to the design of the AirAid Filter, which seems to sit directly in front of the front cool air inlet to the filter, and doesn't allow air to directly flow into the filter.
The system 4DR used before he parted out his Mods and sold his Flex, also came from AirAid. They sell a "Universal Kit" that has pipe that you cut and piece together with connectors ( like I did with mine) that allowed him to extend the filter downward into the fender area behind the headlamp. Here is a link to that kit. There is also another with a shorter filter & same size pipe.
http://www.summitracing.com/parts/aid-101-351/overview/