We went through these with the bad bushfires a few years ago. My main suggestion is pick one where the filters are readily available. Ideally you'll buy a lot more filters than purifiers...

We shopped on ebay, and bought several smaller ones from one of the more recognisable Chinese brands (seems to be a newer model but same filters) that takes a filter that seemed to have more than one manufacturer. I bought extra filters with them, then a year later when we had an idea of how many we used/how long they lasted did a bulk order (10!) and three years later they got us through the worst of the pandemic and I still have a couple left.

(if you want VOC etc removed you need to get activated charcoal filters, plain HEPA ones are not enough - HEPA is a particulate standard)