I had both of these louvers on my old 98 Cobra. My first set were the ABS plastic style. I like them alot. The only problem I had was on route with MCOM to Nashville when they were "sucked" off the car. They were on the car for a long time with no problems. On the day I lost them, I had just left a no touch high pressure car wash. I suspect the "laser wash" lifted the adhesive tabs that held the louvers on.
I tried the aluminum one after this. I didnt like them on my car. They were too squared and rattled alot. I ended up selling them on ebay and bought the plastic ones again. Only this time I used a super glue in addition to the double sided 3M tape.
I still speek with the current owner. It's been about 2 years since i put them on without a problem.
Here is a pic:
