For allergy relief, is an air purifier a good choice? If so what are important factors to consider, choosing?

Answer 1

Yes, an air purifier is a good idea. But, you need to do other things as well.

Eliminate the source of allergans. Some things are obvious, like pets. Also, assuming you're allergic to dust (actually the droppings from dust mites) like many are, than you'll want to get carpet out of your bedroom. Also, look into those special bags for pillows and mattresses. Be aware, the matress ones can make it sound like you're sleeping on a waterproof bed.

Also, ventilate your house or whatever. unless you live right next to a highway, fresh air is a good thing.

As far as the air purifier goes, look at Consumer Reports or something similar for ratings. STAY AWAY from the Ionic Breeze! Those, and any purifier that works solely through ionization, are ineffective and emit ozone, which (when its not high up in the atmosphere filling the ozone layer) is a pollutant. The manufacturers of the Ionic Breeze had to change their design because fo the ozone, but they still are a complete sham.