We have both in our home. The humidifier was a high end purchase we purchased with our HVAC unit. The supposed whole house humidifier has not lived up to what was promised. We still have dry air in our home from the heat of winters and no aromas. Ultrasonic technology is applied in the humidifier and the aroma diffuser; the great difference lies in the details. For the aroma diffuser, the particles can be atomized to nano-grade via vibration while for humidifier the vapor molecules are often bigger, so in moisturizing, the aroma diffuser is the winner.