Ionisers generate ozone in the process of generating charges - there are federal guidelines as to maximum ozone generation permitted.
Apart from potential health issues you have to also take into account increased ozone levels can accelerate corrosion of metals.
Cant wait to see those lovely gold plated SME RG3012 tonearms after a couple of years of ioniser use spewing out ozone in close proximity - should rival all that lovely gear sold after the tsunami a few years ago.