They work eccentrically, resulting in increased vibrations, and have broken bearings - when you hit them, they stop the noise for a moment and then start again. In short, broken from the start. A bad product for a store to sell, no matter how cheap it is.

They break down quite quickly, I have changed 2 in 1.5 years. However, they have high flow. Although noisy at full speed, on a device that controls their speed they are very good.