Serpent have a dyno reading on theirs. Not 100% sure how accurate it is.
I have run one a few times on a big block 15 in a serpent 835. I couldnt tell it was there except I couldnt hear my car over the noise of the other cars on the track.
Performance wise, I didnt notice a thing. My lap times remained the same.
Because of the optimized design, the INS-BOX unit does hardly affect the performance of the engine, it only reduces the induction noise. The performance was measured in various ways: by taking lap-times (no difference), by using data-logger technology (no difference), and on the test bench (approx. 3% difference). What can be felt is a very little loss of throttle response at low speed. But this will be the same for everybody of course. Running the car with or without the INS-BOX has no influence on the setting of the carburetor, which is proof that the air-flow is not restricted.
Using the INS-BOX has no effect on the engine temperature as it does not restrict the airflow and the engine is not running leaner.
It does keep foam dust, dust and crap from getting directly onto your filter, however you would be a fool to use it as a method to negate filter maintenance. It would also be handy for those of you who race in less than dry conditions.