Do these really work?  I have allergies that I keep under control with low dose antihistamines almost daily, and am thinking about some type of indoor air purifier.  Are they essentially junk products or do they really work??

OZONE.  

Consumer’s Reports did a story on air purifiers last year and IIRC none of the ones reviewed had any real benefit.  A few actually polluted the air more with their ozone emissions, which is typical for anything with an electric motor.

I got an Ionic Breeze as gift, and it did work. I figured it was BS when I got it, but I noticed a difference after a few days of using it.  It died after about 2 years, so I got another one.  That one died about a month ago.  

My house is old and drafty, and it definetely helped my allergies. The fins would be covered in dust after about a week.  I read the reports about ozone, but I would rather die of that than suffer with allergies.  I tried a regular air filter unit, but it was too noisey to keep in my bedroom.  I may get another one, but a different brand this time.

I'm going on about 4yrs with an Ionic Breeze.
Once in awhile, maybe twice now, I've had to disassemble for a real good cleaning. Normally you can just wipe down the collector plates which is no big deal.

The breeze does do alot of good, and helps me sleep, without question. I'm not worried nor concerned about ozone. Negative ions kill mold spores which IME is a bigger benefit than any ozone negatives. The cost is one time up front, it does a great job of removing odors (like ode de cooked bacon) and aside from still having to dust the house, it works well.

I can tell you my FIL has serious allergies, in that I mean, prescription medications don't much help, and he hates getting shots... He picked up an Ionic breeze the same time we did, and his allergies chill out at home... But when he's at work for 12hrs, he definitely notices the lack of the breeze.  So I'd say it should help in your situation. You can always try it, and return if you don't like it.

I did have a couple kinds of regular HEPA air purifiers prior to this. They're loud, create cool/cold drafts, and cost a shitload for new filters, which are also hard to find. Yeah, they help with actual dust better, but thats obvious, by design alone.  These are a money pit which, while collecting dust, don't seem to offer much else... at least not for long, the filters get full in a week.

I would suggest buying decent furnace filters if you have forced air heat or AC, and change those a couple times a year.  Vaccum cleaners have some great HEPA features these days, and that would also help I'd imagine... I think these items combined with the Ionic breeze makes better sense and is a more cost effective solution, long term.

Nothing says you can't run a small or medium HEPA filter in conjunction with the Ionic breeze though.
 

of course there is the whole ozone/cancer thing......

Oh, didn't know about the ozone emissions.  Thanks.