You are correct - I hadn't thought of that - but there are so many compact purifiers out there for reasonable prices that I never considered it.
My primary goals in choosing filters, for two homes and our camper, are reputable company, 2 stage filtering (coarse & HEPA) replaceable filters widely available.
We have a whole house filter, then HEPA filters in the main living space (open) and each bedroom. In the guest room we only run it when it is used. Each purifier is sized for the space it covers.