It's possible that they're both crap, although some people swear by them. (And just as many people swear at them.)
The main differences seem to be that the Radio Shack device is $100 cheaper and has a fan. It's possible that that is actually a _negative_ for a product that works on slight electrical charge differences.
And yes, I know that if I really want clean air, I should get a HEPA filter based system, but they're all too loud. I'd rather a silent-less effective system. But I want the least-less effective system I can get.