Infa:
First off, a HEPA is more than enough...all of the other technology is kind of "cherry on top" stuff. With a HEPA, you will not only get CLEAN air, but softly circulated air.
Now, a few small things...
Ozone may be toxic at higher levels, but our bodies are more than equipped to deal with normal amounts. In fact, we HAVE too everyday.
Earth uses ozone (a reaction of oxygen to sunlight in the upper atmosphere) as a kind of constant purification system. The ozone in the atmosphere kills microorganisms and removes molecules (pollution) from the air. This is Earth's HEPA, and we are sitting in it.
Free radicals are 100% impossible to get away from in our warped, polluted society...but (though to a much lesser extent) they would still be if we all lived in forests. In reality though, it is exponentially worse to stand near an intersection (inhaling car fumes) than it is to be in a lightly ozonated environment.
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Now, if I had an ozone generator, would I run it everyday? No. But I'd definitely blast it on max once a month. Ozone cleaned rooms have a "fresh from the dentist" feel, and that's certainly a refreshing way to start the month.
The reasoning here is that a HEPA filter will not rip microoscopic organisms off your walls etc. Many molds (and other stuff) produce Volatile Organic Compounds (VOCs), which are basically the odors you end up smelling. They also have the lovely tendency to be debilitating to human health. Now, if a room isn't infested with mildew, it won't outright smell moldy...but there's still trace VOCs floating from the billions of microbes naturally found indoors. Ozone destroys the VOCs and their producers, making the air "fresher than fresh". Fresh from the dentist indeed.
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A word on ionization:
Sounds: They will only make spark sounds if there's alot of large particles in your air. This should be absolutely nonexistant with any decent HEPA running. Even without a HEPA, the spark sounds are quiet and few/far between (definitely not a constant shocking). Its more like a small fizzling sound really.
Ionization is FAR from being "bad." In fact, everyone here seems to be missing the basic HEALTH benefits:
Positive ions are naturally produced from a variety of things, one of the foremost being anything technological. Your computer, your desk, preamps, phone, etc.
Negative ions are naturally produced by living organisms, most notably plants.
It has been scientifically proven (through numerous studies) that positive ions have a negative effect on human mood. Increased anger, frustration, and depression are just a few highlights. These in turn help create physiological effects like fatigue.
On the alternate, negative ions are proven to enhance mood. Energy levels are increased, stress levels reduced, blood flow is substantially improved, and brain activity is heightened. Hell, why do you think E-Cue is always so happy, and good at what he does? (4 Ionic Breezes? lol...) This (along with natural air filtration) is the actual scientific reason that plants are so important to have indoors, balancing our plastic/metal creations.
Odd bit info here...
Many years after the Russian hockey team was king, it was discovered that they practiced in gyms outfitted with MASSIVE industrial strength negative ion generators. The positive effects were apparently markedly noticabely. Their tour buses? Equipped with industrial strength negative ion generators. Away games? A dozen portable negative ion generators for the locker room.
Its actually kind of getting out of control, as sports groups and whatnot are marketing necklaces, bandanas, and even masks that have ion generators in them. If memory serves me, I believe they are beginning to put very small generators in football helmets and the like.
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Anyhow, to answer about ionizers and debris clinging to your gear:
It shouldn't be an issue with the HEPA filtering 99% of things, and the air flow circulating the unfiltered air TOWARDS the generator. There are, by the way, very easy ways to create an incredibly strong positive attraction in your room (like running a modified plug, with just the ground connector, to a piece of metal or foil...essentially creating a large link to your building's grounding pole). But again, I wouldn't think it'd even be an issue, as the air would be pretty clean as it is.
I'd basically just want the ionizer for health benefits.
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Important to keep in mind, is that essentially these "technologies" (ion, ozone) are nothing new. The Earth has been doing it all in some form or another since the beginning. We're just now figuring out how to replicate it, after we seem to have mastered desecrating it
Anyhow, to restate the opener, these are just "cherry on top" technologies. A HEPA will make a world of difference in and of itself.
I have no opinion on any products, as I do not know their build quality, only what they purport to do.