I own the ION-001. There’s an issue with keeping it on during playback - it degrades the sound. It’s not a huge difference, but once you hear it, you cannot “unhear” it. Highs are rolled-off and the sound loses energy, sounding a bit “muddy”. It may not be discernible on all systems, but on my very high end system, it’s obvious.
It’s therefore not a good idea in all cases, to keep an ionizer on during playback.