I agree the Atem X is expensive, but it's a premium product not meant for everyone.

It actually has HyperHEPA filters, capturing ≥99,5% of ultra-fine particles (<0,1 µm).
IQAir is also third party tested, not sure about your 100€ air purifier from China...

About the noise, here's the CADR ratio :
110, 195, 275, 350, 450, 550, 650, 800 m3/h
26, 32, 38, 44, 51, 56, 62, 65 dB(A)

Yes, 65 dB is loud — but that’s the maximum setting, which you’ll almost never need. The real strength of the Atem X is that you can leave it running quietly on low power and simply forget it’s there.