We bought one of these when I was pregnant with my youngest thinking it would be a good way to solve the problem of me not being able to scoop the box (which I do several times a day because I HATE smelling eau de catbox in anyone's house, especially my own) and my husband would only have to empty it daily.
It worked like a dream--2 cats, no sticking, no stinky odor, great product for us.
The problem? One of my cats was so afraid of it that she refused to use it. REFUSED. She registered this refusal one day by peeing on my brand new sofa. The next day she exhibited her disapproval for the new gadget by pooping in my husband's open briefcase.
Needless to say, we no longer use this item. The most surprising part of the story? The store took it back simply emptied out and repacked into it's original box. I used the credit to my Visa towards a really nice carpet/upholstry shampooer.