The bags are great for bugs and smaller birds, but if your preditor is somethign larger, they will take the whole bag. Not sure if they pop the entire thing in their mouths, or what, but entire bags disappear never to be found.
Still, if you don't have too many fruits, they are better than nothing. And easy to use.
Dry climate here, so no condensation problems. But we have coyotes, possums, raccoons, lotsa big birds, and probably an occasional stray dog.