Hi,
Those are popular with some vintage racers who are running cars fitted with lightweight fiberglass fenders. Last time I looked, in some classes SCCA allows reducing TR2/3/4 to something like 1850 lbs in racing trim (I dunno if their specs are similar for TR6) and thin fiberglass panels go a long way toward putting the car on a diet. But, thin fiberglass can be damaged pretty easily by road debris.
Personally, I'd think twice about putting them on a street car with steel fenders. I would be concerned about dirt and/or moisture getting trapped behind and causing more problems than they prevent. Maybe that's not a concern, if they seal well at th eedges or if they are easily removed for a proper cleaning.