but a friend recommended a different product with a longer diffusing time they ...
I had tried a similar design diffuser by another company that quit working.  Then I tried this one and as soon as I received it, it had a loud higher pitch sound.  The company was very responsive after I sent an audio clip of the sound, indicating it was probably defective.  I might have tried replacing it with another one, but a friend recommended a different product with a longer diffusing time they were happy with, so I have ordered that.
Rating: 3 stars