This will eventually cease to work as many ultrasonic devices tend to. Of the units I used to sell at my place of work, about 85% of them came back within 30 days, 10% of them would be in after 6 months to report that the issue has started again. The remainder either never came back, never said if it worked, or it did work.
I have watched a video on YT about the piezo being used but they didn't state if it was really effective. Thanks.