I have one and mine has 2 suction cups and it holds really well

Penny

The main thing that I don't like about mine is that it doesn't allow for using an ant trap. If move it from window to nearby window, it does discourage the ants. It's not as convient to refill as a feeder hung from a hook on the window frame, which has a built in ant-trap if you use a saucer feeder.
Also, with the feeder on the window, the feeder often blocks your view. I generally block all the ports but one on a feeder, so that the bird will come directly to the spot where I can best observe/photograph him, and not "hide" behind the feeder.

Here is a link that might be useful: My Spring 2003 Hummingbird photos

I used to use a plastic one with 2 suction cups and it held very nicely. It helps to put it up on a clean window and lightly moisten the suction cups when placing them on the window. Robin

I put up two window feeders this year, and they are both getting used! They don't have an ant moat, but they haven't been discovered by the ants yet, either. I did read to put double sided tape around where you put up your window feeder, as a way to deter the ants. Haven't tried it yet, but I plan to give it a shot if necessary! Hope this helps!! Christy

This has been my favorite window feeder

Here is a link that might be useful: window hummer feeder