At least some of them don't really work at all. https://www.youtube.com/watch?v=VM9CJZpqfpA

With something as simple and effective as HEPA-filters, it seems unreasonable to try other technologies.

Many (most?) proper ones use a combination of a coarse washable pre-filter, charcoal, HEPA, and ionizer. Which makes sense, since they all basically do different things.