I have one and never liked it. First off, it's kind of cheaply made.. 2nd, the grate doesn't fit firmly in the frame so Tuffy would always grab it and play with it.. 3rd, it's proportioned to use with newspapers, not pee pads and I don't like using newspapers becauses they aren't absorbant enough and have to be changed more frequently. 4th, when they have runny poops, it will get all stuck in the grate.. luckily mine never used it for us to have that specific problem. Basically, I wasn't impressed with it.. don't get me wrong, the idea is fantastic, but the actual product isn't that great. JMHO. Here's a picture of it up close because I don't think the website does a very good job of showing you what the actual grate looks like:
http://www.pluschic.com/wizdog.JPG
I've been looking at this product from Puppy In Style and it seems to be a more well made one. It's also cheaper than the Wizdog.
Yogi Puppy Toilet