They're ok, but feed can get stuck in the bottom of the spiral and spoil if it gets wet (particularly pellets, less so grain).
Before you spend any money though, try drilling a hole in the bottom of the barrel just big enough that feed only comes out in little drips when pecked.
The reason I say this is that I made a feeder similar to the trigger feeders you can buy (see
this thread for more info). It works perfectly, but the hens actually prefer to peck at the hole in the barrel, rather than the trigger. This makes me think that it must be possible to do away with the trigger entirely. Worth a thought at least?