Ionizing air purifiers are a hot commodity, but they promise much more than they can deliver on. It turns out that many models are actually harmful due to high levels of ozone generation. Consumer Reports did studies in their labs that determined which models were producing these dangerous side effects : See this pdf from Consumer Reports for more information.
The LA times also reported on the subject and quoted immunologist and allergist Dr. James Sublett as saying “Ionic air purifiers have undeniable appeal, but there’s a problem: They don’t really improve air quality, we [allergists and immunologists] generally don’t recommend them.” The article goes on to explain how the ionizers only work in the immediate surroundings if they have no fan (less than 2ft), and even if the ionizing air purifiers have a fan they quickly lose effectiveness as the plates get covered in dust.
You can find the LA times article here.
tl;dr : Be weary of Ion only solutions because they don’t really improve air quality.