Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Beware of quality control

Ran unit in a small dusty room for 12 hours- with and without ionizer on- and after 12 hours on 'high', the filters were absolutely clean. NO DUST ACCUMULATED AT ALL in filters. Very weak airflow into filters, although outflow was strong. Returned it and will try another brand.I bought this item because there were so many 5 star reviews...I guess that the quality control from the company is the problem, since there seem to be units that are absolutely useless and some that work great. Wish I'd gotten one of the good ones.