Are you using a stock or aftermarket air filter?Bought the RS intake from my local Ford Dealership for $67. It took two days to ship from another dealership 30 miles away. Installation was a piece of cake and I'm totally happy with how it looks and sounds.
Taking the lid off the stock air box is too loud and boomy in the cabin, but having this airbox installed is a nice balance between that and stock. It's only loud when applying medium to full throttle from 3000-4500 RPM or so but can be completely quiet, just like stock, when cruising around town or on the highway. It's the best of both worlds. I really like how it sounds.
As for performance, I doubt it makes a difference. It's more for the sound and appearance. Worth the money in my opinion.
I definitely noticed a major performance increase with the complete RS airbox swap & Mountune open end filter, but I also did the snorkel delete and removed the airbox resonator. I have to say it pulls very strong from 80-120 on a closed course. I've been hoping to find a ST to run beside for comparison, everyone I've seen has been driven slower than my grandmother drives..