I used this kind of rods years ago and now I needed to buy more. This ones are of good quality so I'm going to order more.
I find this kind of rods very useful when you don't want to drill the walls. They are not to be used with heavy curtains, but they are perfect for sheer curtains, which by the way, are the adequate ones as the rod is placed very near the glass. The rod is telescopic and you just place it between opposite (and parallel) sides of the window frame/walls and unscrew it until it feels tight. They don't damage nor leave any mark on the frame and can be reused for different windows as you can adjust its size between the minimum and max indicated for each rod.
Try to choose the rod whose minimum size is closer to the window's size, because the rod is much stronger when "closed" and becomes weaker when extended to its full length.