I found similar at the UK take, Which. Everything is boiled down to star ratings and then Mail Merge creates the review text.
Apparently, each air purifier which can handle a large room is big, heavy and loud. And the air purifiers that score highly on being quiet have the downside that they can only handle small rooms. Oh, and they did measure the CADR, and will tell you that "this air purifier scored five stars on our CADR test".
For air purifiers, if cost is no constraint, my IQAir GC has worked like a champ. The lower three speeds are reasonably quiet, and speed 6 cleans out the room in no time when my partner burns the cooking. Comes with a 10 year warranty.
Keep in mind air purifiers are just a fan with filters in front of it. A box fan with a furnace filter strapped to it, while ugly, will do similarly for reducing the amount of particles in the room.
What you're paying for is basically three things: a design that looks acceptable in a room, a fan that's reasonably quiet, and ability to source filters in the future.
Check, check and check. And also a filter quality and seal design that's been tested and proven to work (they do a QA particulate test on each individual unit before it ships https://imgur.com/a/exTrjU7).
Apparently, each air purifier which can handle a large room is big, heavy and loud. And the air purifiers that score highly on being quiet have the downside that they can only handle small rooms. Oh, and they did measure the CADR, and will tell you that "this air purifier scored five stars on our CADR test".