PRO: IMHO, the best bang for the buck. For this price range, you can never get a headphone with this accuracy. (The helmholtz resonator equalization is brilliant!) Moreover, the distortion figure is beautiful- it is almost non-existent.
CON: MC5's frequency response bandwidth is quite limited, compared to Etymotic's reference model, ER4. Still, the headphone performs much better than other dynamic driver-equipped IEMs!
ON SECOND THOUGHT: There is a way to extend the frequency response bandwidth, by using different ear sleeves. Changing the quarter-wavelength resonant property by modifying the length & diameter of the bore will effectively shift & distribute peaks evenly- Here is the detail.