I know Blaine doesn't like them and says they don't produce 'shade'.
They do block some of the sun which reduces the amount of direct sunlight which reduces the amount of heat felt.
No different than a pergola or lattice over a patio.
I would also say it blocks air flow. It may not reduce the turbulence, but it would direct air over it more than through it.
IMO, there is a noticeable difference.
What people have to remember is they work differently in different parts of the country- They may not be as popular in southern California or Arizona where it gets extremely hot but in temperate climate they are fantastic and they can keep you from burning alive at a red light-