The Box is 90% of the install. Radiused corners would make for a cleaner and easier install of the rubber seal. Is the seal intended to seal against the underside of hood? Is there a trick to doing this? Quality of materials very good. Increase in performace/mileage is hard to measure. Probably avoiding the "conch shell call" sound means your getting better economy. I miss the cast "Hemi" cover. Likely best unit on market. Necessary? Not really. Fun? Okay.