They are great, the suction cups are okay, the do withstand rather strong winds. I use a desk perforator to make the right size holes. Make sure to cut them to the right size with a slat of wood on top of the material and using a very sharp boxcutter. make sure the suction cups are not to close to the edges, at least 5cm inward. Make sure your windows are clean before applying suction cups.
This really cuts down the temperature in my house on warm days.