I have a 3 1/2 year old Boxer that barks, cries, whines, and howls when I go to work...ALL DAY...I know, I recorded it. I went online and picked this gadget. I got it home and hit the manual correct button. She bolted. She hates the ultrasonic noise that it makes. It reduced the amount of noise that my dog makes but only in a certain area and I don't lock my dog away when I'm going to be outfor more than 8 hours.
So if I'm just running out for a few hours I stick her in her crate with this right in front of her but if I'm going to work I use it in conjunction with the petsafe electric shock bark collar.
My girlfriends dog does not really notice it if he's otherwise engaged but my dog hates it. Worth the price in my opinion. Best advice is to take it home and try it.