dōTERRA Pebble™ Diffuser

I purchased 2 of the Pebbles. Neither worked. Returned them. 2 others were sent to me for which I thank you. After a couple of weeks, one of them is no longer working. I will send this back. And,,,,, hope for the best with the remaining Pebble that's presently working. They are little, and cute. Functionally, ??? Great for small spaces.