Especially in residential buildings, air cleaners/purifiers can be useful tools in improving the Indoor Air Quality of your rooms in addition to mechanical ventilation systems.
However, not each of these products does what it promises. In some cases, the wrong air cleaner can even worsen your air quality.
Ensure that you only invest in state-of-the-art equipment with high quality and exchangeable air filters. It might be a bit more expensive, but will pay off in the mid- and long-term.