If you are not allergic, then no need worry about... Ionizers is not a important feature that you should looks into. Choosing a good purifier, the first priority things is the CADR (Clean Air Delivery Rate) that capable to filter. And does the HEPA filter, is it able to filter PM2.5 (Particulate Matter).

Because that is the basic standard of what an air purifier should be. Ionizer is extra feature.

Just like water purifier, it must able to remove all unwanted stuff from the water while retain what should have in the water. Hot and cold feature is additional/optional feature.

A air conditioning should able to produce cold air, ionizer also additional features.

Boiler should able to boil water, keep warm or able to make Coffee is additional features.

So, TLDR? Look for a air purifier with Hepa features that capable to filter PM2.5 and high CADR. Check the Hepa filter micron. If need to filter VOC stuff, you need a filter call carbon filter.

Agreed. Actually I also find it damn cheap. Was thinking how to buy. Why I said cheap?
Take Sharp for example. To filter the same area, price is about Rm2k+. This only RM800. Also, you won't be using it every day. Just when got haze only. Hence the filter should be able to last a year. So we do not need to change it every 6 months like what xiaomi recommends. Once a year should be OK.

Even though sharp filter needs changing every 3-5 years, this is still cheaper.

Your body have it's own defense system which is pretty effective against most common germs. There are ways to increase it naturally so that one does not get sick easily. However if you have HIV, then is different where your immune system is totally not functioning.

Your immune system can get rid of virus on its own but not haze particles. So one should give the immune system a boost for haze. The rest let it take care of itself.