mild2wild NPP exhaust converter.. good or bad?
 

I just installed this on my car with 500 or so miles. Sounds much better at low rpms and idle. Up top sounds the same. My question is: Is it bad to always leave on "wild"? Does it hurt the car at all in any way? i noticed when revving it stock its clean, when revving it in "wild" i get a touch of black smoke and I only run from known gas stations... Should this setting be a just and a once and awhile thing? Also loses a lot of back pressure.. pops a ton on decel...