Disclaimer: This is the biggest surprise from Inks' stimulus package!
松尾伴大-san, who is the developer of MDR-EX1000 and the 5th ear mold master of Sony, states EX-series is designed to be as acoustically transparent as possible, by utilizing the essence of Sony's moving-coil driver technology, so that musicians and Hi-Fidelity enthusiasts can enjoy the sound quality alike. And although MDR-EX210 is just one of those random introductory models of the series, I see a great potential in it.
CON: The overall tonal balance is quite bassy. The vent located at the bottom of the housing is simply a depressurizer.
ON SECOND THOUGHT #3: It seem EX210 shares the same acoustic design with the flagship model of EX-series, MDR-EX1000. Not only most of resonant characteristics in the treble well-match, but also the high frequency extension of the two corresponds to one another. If an acoustic vent can be introduced on the housing of EX210 and reduce the level of bass by 9 dB, EX210's tonality shall become very close to that of EX1000. I definitely see a great chance for modification here.
ON SECOND THOUGHT #4: The IEM is too bass-heavy to be considered as Hi-Fidelity, at least in its stock configuration.