Make sure you get a Purifier with air quality sensor, otherwise you won't know if it is doing anything.
Overall good ventilation is best; however temperature and or outdoor air quality complicates this.
I think they are best used sporadically when needed. For example during warmer months, I never use it, just leave windows open. However during Winter I noticed the air quality getting quite bad inside, especially VOCs, and so running the air filter with charcoal and hepa (no UV or Ionizer) greatly improved quality.
Also it's shown running water helps clean air; this could be a budget option get a small water fountain setup at home and let it run constantly, maybe paired with just an air quality sensor to monitor things.