Air purifiers: good or fad?

I live in a stone built converted chapel.
It gets damp easily for reasons I cannot address.
This causes mould to grow, especially in winter and when I am away for a few days/weeks as the heating is not on.
Currently pondering an air purifier to remove mould and mould spores. I also have a cat, apparently, it helps with dust and dander too.
They aren't cheap! And there seem to be so many.
Any Fetchies who have personal experience?
I do have multiple allergies, so I think "pure" air wou...