I have a Stage FP for 2 summers on my N51, last mo flashed to oem for emission test and got the contrast of flash back last Wed. In my research if I was doing headers and performance exhaust I'd prob done AA. My desire is lite mod with leaving it the spirit of OEM yet snappy. No loud exhaust or turn it up to eleven compression, mainly improved throttle or faster response. Worth every penny
Stage FP cons-
the startup on oem has a warm-up lasting 5-45sec depending on how warm and ready the engine is. In spring and fall in the Chicago area I get cold start stalls with Stage FP installed. I can manually mimic the oem warm-up most times however if I toss the key to a buddy to move or drive forgetting to tell them about it, panic phone call or text- worried I broke your car apology. Summer and winter startup is just fine.