Slinkies can be pretty effective as long as the feeders are too high for the squirrels to jump to. Is that a plastic slinky, though? They might chew through it if they get really frustrated! Of course, frustrating squirrels is an art in itself and success might be worth the price of having to replace a few plastic slinkies.
The old metal ones work better, but they're really hard to find these days.
For $8.02, how can you go wrong, though?
You'll have to give us a report in a few weeks and tell us how it's going. I may have to steal your design and put one up for the sunflower heart feeder. The squirrels and raccoons both find the hearts to be pretty tasty. Wouldn't mind it too much, since both animals are pretty entertaining to watch, but it's the most expensive seed I use and they're snarfing it up like it's going out of style!