Yes IQ is the best. But I wouldn't say the cheaper ones from Fortress do "essentially nothing".
My friend had IQ come and test the air quality in his flat prior to purchasing an IQ. The pollutants in the main living area were around 300000 ppm. However in one of the bedrooms he had a Sharp Hepa/Charcoal unit from Fortress and the reading was around 60000 ppm. I think the IQ ones are guarenteed to get it below 25000 ppm, so they are better, but the Sharp air cleaners significantly improve the air quality at a fraction of the cost.