Air Purifiers

I have severe allergies and I am looking for something to help. What is the difference between these two things?

If i put it in the corner or near the wall. How is it going to suck in any air. the air is sucked in from the back. if its facing the wall or a corner. it wont get all that air in front of it (basically the whole room)

It is recommended that you keep it a foot away from a wall. But since it sucks in air from the back, won’t it not get enough air cuz its facing the wall so closely

Where can I find a good but fairly affordable negative ion/ozone air purifier for my parents for Christmas?

I am looking to buy an air purifier. I have a fairly small apartment. So I am looking to freshen it up a bit. I dont really want to spend more than 0. I saw the ficus tree one and it looks nice since it looks like a plant. Any suggestions?
http://www.target.com/gp/detail.html/602-3205341-1476617?asin=B0009F59I4&AFID=Froogle&LNM=B0009F59I4|Ficus_Tree_Air_Purifier&nAID=14110944&ref=tgt_adv_XSG10001

The device is filtering air, but I had read that negative ions generally lead to a lot of dust accumulation on furniture, walls, etc. I dont see any evidence of dust accumulation. Am staying in a very polluted environment and just wanted to ensure the thing is working.

I just bought a home and the previous owners were not very clean. My home has a foul odor. Or could it be my vents in the A/C.
Should I buy a purifier? (please recommend a good product), or clean the vents or BOTH (yikes!)

I need an air cleaner in eliminating pet particles, mold, dust mites, smoke, gases, etc.; preferably one that has a filter that can be just wiped off and put back in or filters that are not real expensive. I have heard that Carrier Air Purifers are the best but just not sure. Looking to clean/purify approx. 800 sq. ft. And does an air cleaner eliminate radon or others gases that possibly could be in a basement?

I learned that the Sharp air purifiers’ HEPA filters have an Apatite component to it that apparently provides antibacterial properties to protect the filters from microbial accumulation. Is Apatite a relatively "safe" material to use for an air filter, i.e. is it safe for the resident who is breathing air that comes through the filter? Apatite (a very general term) is usually made up of phosphorus and calcium, but some variants (ie. arsenates like mimemite) may contain arsenic. Could this be a health issue for users? Would the filters use arsenic-based variants in the first place, or are other forms more prevalent and likely to be used in medical/industrial applications?

Do they cause cancer?

I have very bad air where I live. Also, dust and mold allergies. Anything that can get rid of those things would be great. Thanks.
i wish i could. but the city has a lot to offer.