We don't have tinted windows on our car so the sun can be very unforgiving, especially during the summer time.
I have a toddler who rides in the back of our Mazda 3 and I usually sit right beside him while my husband drives. It's bad enough that my toddler gets warm from just being in his car seat, so imagine him during the summer with the sun's rays shining directly on him. We used to use those car shades that suction cup on to the window and while they worked for the most part, they still left areas uncovered. This is why I love this type of car shade. It slips over the window of the car, like a sock, so it covers the entire window. You can even open the windows with them on. Couldn't do that with the suction cup shades. Also, it helps to keep the inside of the car a little bit cooler, and keeps my son's car seat from being too hot. I like that it has a Velcro strap that you have to stick onto the frame of the door. Not entirely sure if it's needed but it may help to keep the shade taut and in place. Since you have to stick one half of the Velcro part onto the door I don't know if that will last very long with the heat of summer. But we'll see. It's made of a mesh material so it's breathable. I like that it's washable too. It can get difficult to see through during the night, so if you're worried about the blindspots you can just take it off at night.
These shades are a lifesaver for my toddler, and for me too, since I sit in the back with him and can feel the difference. Sucks for my husband up front braving the rays of the sun though.