I have a pair of Electrolux EAP300s, in small rooms.
Unfortunately on the lowest manual setting ("Quiet") they hardly do anything for air quality. And they're still louder than I like. I think they really optimized for cost; these devices feel very light and plasticy, the fan sounds cheap and has an uneven tone to it, and its speed keeps oscillating back and forth. The purifier itself is also not stable and it can make an annoying noise if placed on a surface that ends up vibrating along.
I also thought about DIYing one with noctua fans (which I know are quiet, and I have plenty of them in my PCs), but I suspect they're not going to be very effective.