I contacted Weathertech and they said they would ship me a set of clips for the rear. It would make me feel better having them there.
Here are some pictures of the Weathertech visors installed on my car right now without the clips.
I only took it from one side, but you can see how streamlined they are. They don't stick out much at all.
Here's what they look like if you were walking up to your car to get in.
Overall, I like the look a lot and it allows me to crack the window when it rains. I've always had visors on my cars and I was told by fellow racers when I lived in Japan that they are good to have. It allows air to get into the car so you don't run your AC while maintaining decent aerodynamics. I have no proof of that, but it makes sense.