Easy to use, a drill-free hit!
This was really useful as our windowsills are too small for my cat to comfortably spy on neighbourhood squirrels and birds. The only drawback was that requires some depth of windowsill on the bottom and the top. It wouldn’t fit one windowsill that had only a few centimeters depth on the bottom, and the other ones I had to flip the brackets upside down as the radiators are too close below. But once I flipped it, it’s been a very handy way to provide good window space without drilling holes.