The Wyndmere Classic DIF433 bills itself as an "ultrasonic nebulizer," which is tech-speak for saying that it does what the vast majority of automated oil diffusers do: Blast a fluid (in this case water with a few drops of essential oil added) with an ultrasonic wave that breaks it up into droplets so tiny they can float on air and make a room smell nice. The great thing about ultrasound is that it's so ultra that only your dogs are likely to hear it; it's way out of the range of human hearing. The Classic, an attractive, round unit with a transparent, lamp-like lid, will also glow in soft LED colors that can be used as a night light or just as a mood light for dimly lit rooms. When set to continuous release mode, it will give you five hours of aromatherapy, which is a good but not extraordinary amount.
None of this explains why the Classic is currently available at unusually high prices for an automated oil diffuser, especially given that some online users describe it as "cheaply made," so you might want to shop around for a used model or one being sold at a bargain close-out price. Users seem to be mixed on its reliability, with some claiming they got months of use and others that it broke down after a few days. And there's at least one complaint about the beeping noise it makes when it runs out of liquid, an odd thing for a night light to do.
An interesting note from one user says that, if it stops working, it will start again if left unplugged for 24 hours, but this seems like a lot of work for the price. If you want something with more of a reputation for reliability, you might want to go elsewhere, perhaps looking at Homedic's Ellia line of oil diffusers, which includes the Awaken, the Reflect and the Gather. Or look at some units from other competitors, like the Pilgrim Sofia Waterless, the Green Air Spa Vapor 2.0 or the Welledia Wellspring.
It's very easy to clean, and does not retain fragrance from essential oils that I have used.
My only complaint is that you can't turn the sound off. I have this set to run all night and when it auto-shuts off there is a loud beeping sound that will wake me up.