Depending on your driving style and where you live, the dust shields can become dangerous. Even with the cooling slots, they are still not introducing enough cool air to the calipers and rotors to keep them with in operating temperature. Especially during the summer when the temperature outside is really hot, it will cook your brakes faster, which can reduce brake pad and rotor life. Also under extreme circumstances it can cook the brake fluid in the caliper causing air pockets to develop which in turn causes you to get a spongy pedal, or loss of pedal feel.
I had them on my BMW for a week, until I lost the brakes due to over heating them.
The reason why Wheels have openings in them is not just for looks, they have a function and that is to cool the brakes.
I would not recommend the use of them!