On the one, the perches are mounted to a cage that is attached to a spring. If anything heavier than your typical feathered friends get on it, the spring stretches, the cage drops and some decorative metal leaves block the holes. Once the intruder jumps off, the spring retracts and it returns to normal.

On the other, there's a single perch bar with a counterweight attached. The food comes out in a tray in front of the perch. If anything heavy gets on that, the perch tilts down. If they manage to hang on, it also covers the tray. That was the one that an intrepid squirrel managed to get into after much effort. He didn't get much before he fell off. He stood there and looked at it and I could almost imagine him thinking "S O a B" Had a crow land on it one time and he swung upside down before plopping on the ground. He was not pleased either. You can adjust the counterweight on it as well if you want to keep larger birds off but I've never tried it. They're both only about 3 feet off the ground hanging from a 2x4 crossbar attached to a 5' 4x4 so it's not like they can't get to them.

The first one was the "Perky-Pet Wildbird Squirrel-Be-Gone" and the other was the Squirrel Be Gone II. If I were to rate them I would give the first one 9 out of 10 and the other a 7 out of 10. The only issue with the first one was a flimsy hanger that I replaced with some heavy gauge wire and the other, well, a squirrel did get into it although they leave it alone 95% of the time.

I've had one similar to the picture and while ours was squirrel proof, it was also as rhizo_1 mentioned, bird-proof. The one I bought had a suet feeder in it. The first suet cake I put in ended up about 5% eaten and the rest turned to rock. I made it into an improvised bike basket for our granddaughter.

The squirrels have to be content with scavenging on the ground, or what I throw out there for them, because they can't get to the feeders. Like CJC, my feeders are mounted on poles with squirrel/raccoon baffles. They are 6-10 feet away from surrounding shrubbery or trees so the squirrels can't jump to them. This has successfully kept off the squirrels, chipmunks and raccoons - although they try to climb up the pole sometimes, they can't get past the baffles.