I used to use one of those and really couldn't tell much difference. I think it keeps the sun off the interior a little better but I have never had a dash crack anyway therefore its a waste of time and money for me to mess with them.
I bought the cheap ones at Walmart and it makes a difference. I have a solid black truck and a red Camry with black interior. With out the windshield shade I can't even touch the steering wheel on the Camry. For $8 they work.
Of course they work. It's science not magic. If you can reflect the sun out of the car vs it beating down on interior pieces which soak up the heat, it will be cooler. The trick is you want to park facing the sun if you use one.
I have the Covercraft UVS100 custom sunshade. It definitely works, especially if you park facing the sun. I started out using it year 'round, but now only use it in the summer months (saw no benefit to it in the winter months.) Takes less than a minute to put it up and remove it. Custom fit is the way to go. Fits perfectly and you don't have to fight with it. The universal ones can sometimes be a real handful trying to wrestle into the window.
We sell the Intro-Tech ones here and they are awesome. I have them for my cars and use it almost every day in the Mustang. I just wish they made side ones since where I part the sun is on the driver's side of the car most of the time.
At work I park in an assigned spot. Monday at 5:00 I started up the Mustang and had to wait 5 minutes before I could even touch the steering wheel it was so hot. Tuesday at lunch I went to NAPA and bought an $8 silver sunshade. Went out to my car at 5:00 yesterday and the steering wheel was only around 100 degrees! $8 on sale, well worth it in my cheap opinion.
I use the 2 piece type available at WM ($8-10) and have them in every vehicle. I like the 2 rectangular shaped pieces since they can be used on most any windshield size, simply turn the pieces the wide or tall way to accommodate different sizes. Definitely reduce the inside temps and preserve the dash.
Yep along with good quality window tinting on the other windows they're GTG
Up in rainville not so much of an issue but when we road trip down through the desert in summer the combo keeps the interior at "holy [censored] that's toasty" instead of "I am sitting in the surface of the sun."
Sunlight is reflected off these shields, and the brighter the reflection the greater the energy bounced away. So yes the chrome shiny ones do a good job reflecting energy, not sure how much better than other colors. But if the car sits in the sun long enough it will still get hot inside. There's no way to completely keep out the sun's rays.
I have found for short term (2-3 hours) they make a big difference in how hot the interior gets, but for all day, interior temps not much difference, but steering wheel, dash and interior are more protected from UV, so less fade and cracking, and steering wheel no where near as hot.
A good window tint also makes a big difference.