This Birds Choice Hangup is well crafted and seems very strong. It's made of super-strong UV stabilized polycarbanate, measures H 9 in, W 13 in, D 2.5 in, and claims it won't crack, yellow or peel, and can hold up to 3 lbs. 
The instructions were really easy, it's recommend to clean the window prior to installing,  soak the suction cups for two minutes in warm water before applying to the window, then press the suction cups. Pushing on the cups a few times releases the trapped air, and your done. It is recommended to occasionally check the adherence of the hook to insure it remains securely attached. The hanger can be mounted hook up or down, what ever your preference or need to accommodate your plant. 
I love this hook not only is it great for humming bird feeders,and plants but can be useful for hanging holiday decorations, wreaths and so many other decorative ideas.