I had Synergistic active shields in two systems over perhaps a couple years, always preferred them on. I never heard any damping, veiling, quite the contrary, always lowered the noise floor and opened things up. I always plugged mine into power conditioners, perhaps that made a difference. Ted has the tube conditioner/power unit out now, it reportedly makes a large difference.
Still, if you prefer them off and like the sound, why be dissatisfied.
Still, if you prefer them off and like the sound, why be dissatisfied.