Re: Thoughts on home air purifiers
Two quick things.
First of all, I looked up the guy you mention - he seems credible, but I think you may have misinterpreted his comments. I found a lengthy article he wrote explaining the different types of filtering systems available and he actually recommends the use of air cleaners with a true HEPA filter, particularly those with a gasketed filter. He rails against manufacturers who try to pass off cheaper inferior products as "HEPA type" and gives pretty detailed explanations as to what makes an effective HEPA filter (and which types aren't as effective as they should be because of manufacturer shortcuts, etc).
At the end of the article he specifically says that his remarks should not be interpreted as "badmouthing" HEPA air purifiers and recommends them as the basic foundation for good air purification.
Second, I think you have to identify the thing (or things) that is causing you trouble so that you can focus on limiting or eliminating your exposure to it. This whole struggle against allergies is a lot more manageable if you know the "enemy" you're fighting because it's nearly impossible to eliminate all allergen exposure. For example, if molds are the issue (which might well be the case if you have more issues inside than outside), and your home has active mold growth in the carpet, an air purifier won't solve the problem - it may help some but you'll have to figure out how to address the underlying issue.