Smart Air (Distributed by SmarterHEPA) - Sqair Air Purifier

They can be helpful. I bought the Sqair air purifier from Clean Air (they have a partner shop in F-10 above Juice Land where I got it from though you could also buy from their website). The only thing you need is HEPA filter in an air purifier and also see whether it'll be enough to cover your room size. Sqair is noisy at high power though but you could leave it on at medium power throughout the day/night. 

We love Smart Air: https://smartairfilters.com/en/product/sqair-air-purifier/

I have been using smartair sqair since past 3 years. Imo most cost effective purifier, but it does not monitor aqi and doesnt have an auto mode. For monitoring i use ikea vindstyrka.

As sonic says, the Aranet is the most common one. I have the one sold by SmartAir (https://smartairfilters.com/uk/en/product/qp-lite-air-quality-monitor/) that was a bit less expensive. SmartAir also makes purifiers of various sizes. I have a Sqair in my office (they also have the QT3 portable one, but like other people, I'm not convinced by the bubble filter idea, so I prefer to mask).

I’ve been using SmartAir purifiers for about 7 years. Used the filter strapped to a fan model until they stopped carrying them and transitioned to the Squair. I have one at the office, and one in my kid’s room. I replace the filters the first week of November and maybe again in February (depends on how they look). They have, by far, the best cost to performance ratio of any purifier. And they’re pretty good about having filters and parts available, which can’t be said for most Emart or BSB options. The only other brand I’ve seen that consistently has replacement parts and is of good quality is IQ Air, but they’re orders of magnitude more expensive. My parents purchased one for my family when we moved to Mongolia - it stays in the main room and cleans the whole apt. I’d have never paid that much for one on my own. I replace the pre-filter and hepa filter but not the carbon filter each November. The purifiers run 24/7 from November to March and I vacuum the filters about every other week.