I've tried a number of other suction window hangers, but none held up the way these hooks do. I use them to hang up bird feeders with nectar for hummingbirds spring to fall and with bird seed for the other birds the rest of the year. These hangers work great!  Even when a large bird such as a northern flicker or jay lands on the feeder or on top of the hook, the suction cups are strong enough to keep the feeder firmly attached to the window. I've purchased them for friends too.