well thats partially true. first off, its not K n N filter. i mean its not original for sure cuz original costs like 5 times that much. but yes, gud quality chinese stuff is for that much. n yes the filter last longer then the regular one but its not as simple as that. every 10k kms or so, u ll have to wash the filter with soap or shampoo solution. for that u ll have to take it off of the engine.
another point is that generally it is believed that these cold air intake (not necessarily cold air but still) dont filter the air quite well. so u might have to get ur throttle body cleaned often.
the mileage may or may not increase. infact in most cases mileage decreases, as the intake lets more air (and sometimes, denser air) get into the engine, more fuel is added/needed. so the car runs a richer mixture n mileage decreases. it can be, however, tuned to give gud mileage.
this filter would not work well with CNG incase we start getting it.
the only gud thing is that it will enhance the performance by noticable difference. plus it will give a loud sound everytime u accelerate, which is a gud thing for a sportier car. performance is basically the primary purpose of getting the air intake n if thats not what u are looking for, i'd advise u to stay away from it.