Got my
heat shield from Toyotapartsoutlet. Never owned one of these for a previous car, but since the FR-S spends weekdays out of doors and with the black interior, I came to realize it was a necessity.
I had used similar "shields" previously in airplanes where their use is pretty common with small aircraft because they spend their lives in the sun, and have lots of expensive electronics in them so I knew they worked.
So far, I've been happy with it. It definitely decreases the temperature inside the car at the end of the day by probably 20 degrees or so. Not sure about the 40 degrees listed on the product itself though. More importantly I can tell just by being able to touch the steering wheel without leaving blisters its working!
It does tend to sag a bit in the middle, as you can see in the picture below, but otherwise fits perfectly and becomes easier to roll up after some use. Still have to fiddle with it a bit to get it down to the size the velcro attachment has.