Not bad but not great. Even with three times the recommended amount of essential oil the scent only lasted about 30 minutes. By the way I was using lavender and orange for a nice relaxing/ unwinding scent for the bedroom, I was also in and out the room while cooking and doing other house chores. When I had finished and got to my bedroom (around 30 minutes later) the diffuser was at least 3/4 full of water still ( I normally use 300ml from the start, so at least 200ml left) but the smoke/ vapors coming from the machine didn't smell of anything.
I'm not sure if its the same with all diffusers or just this one.