I just got one of these off of Ebay for about $35, I was tired of the squirrels emptying the bird feeder in a day. The thing is great. It doesn't hurt the squirrels at all, the get a little spin and then jump off, they usually manage to get a seed or two but they can't empty the whole feeder. It's entertaining to watch all of the ways the squirrel tries to defeat it. A lot of the squirrels in the area seem to already know what it is and they don't go near the feeder anymore.
Ali
Ali