However, plants can have psychological benefits, and they give off a certain amount of oxygen, so there are still good reasons to have them indoors. Removing formaldehyde just may not be one of the reasons. The air fresheners sold in grocery stores do not clean the air. They simply add additional scents that either cover up air pollution or deaden your sense of smell. This can give you a false sense of security if you believe that the pollutants have gone away.
Many manufacturers offer air cleaning devices that combine two or more different filter types.
For individuals with conventional allergies to things like dust mites, pollen, or mold, a medium efficiency filter, either electronic or mechanical, can do a reasonable job. HEPA filters are of course much better, but they can cost more also. For removing gases, the portable filters are an easy solution, because whole house adsorption filter systems, that are a part of the heating system, are costly. The very small portable filters that are designed to sit on a desktop are probably not worth considering because they simply have too little capacity. Most room sized units are just that - they will only work well in a single room, usually up to 200 square feet.