In reply to Siward:
> The basic cage ones actually work, last for years and allow lots of birds access at once.
They also provide a degree of protection from predators - most specifically sparrowhawks (reference Trangia's comment). That said, I have no problem with a sparrowhawk finding occasional sustenance in my garden. I use a cone-shaped squirrel baffle as recommended by Ron Rees Davies. On the feeder I have hanging from a tree branch I have a rather wider dome-shaped baffle which keeps the squirrels off.
I tried one of the "trick" ones with the spring-loaded perches. It did work, in that it denied squirrels access to the bird food, but I found that the birds weren't keen on it either. Which rather defeated the object.
I also tried a squirrel feeder like this one https://images-na.ssl-images-amazon.com/images/I/81nsKGeNFxL._SL1500_.jpg which I filled with peanuts. The idea being to try to keep them off the birds' food by giving them their own source. However, after watching one squirrel empty the feeder in a morning - taking the nuts away to stash somewhere, presumably, since it involved a lot of coming and going, it wasn't just sitting there stuffing its face - I gave up on appeasement and have since focused on prevention.