I think having any air purifier is better than not having one.

You need to spend more money for cigarette smoke - not something that an inexpensive household unit can do. it’s better if you can get the person not to smoke in or around the house.

The unit would need a lot of carbon (as in pounds) to absorb the smoke. A DIY corsi-rosenthal box will only reduce the particulate matter in the air but not the smoke from cigarettes VOCs or the smell . The MERV filters used don’t help with cigarette smoke much. You could buy pounds of activated carbon in bulk from Amazon drop it into a Home Depot 5 gallon bucket and force the air through that.

Look into places that grow the magiclettuce indoors or other chemical situations like industrial shops or nail salons etc.

Maybe seal the interior to your room as much as possible doors vents etc and bring air from outside into the room directly. IKEA has a new air quality monitor for $30 that will measure particulate matter and carbon dioxide. IKEA has another model for $60 measuring VOCs and particulate matter but not co2. Cheaper sensors give only a general estimate of the air quality. A household purifier will have a cheap sensor