this is a simple and economical product that does what I needed:getting rid of those nasty savage house sparrows but keeping my house finches. Another pro is that it attracted pine siskins. I used to get some pretty crafty pigeons with my window mounted trough feeders now they have ZERO interest in these. Yay!! I live in an apartment in San Francisco and have a park across the street and have a somewhat limited supply of birds but they will find these sock feeders and spend plenty of time using them. Buy a big bag of nyjer seed (I keep mine in the freezer) and fill the bags as needed. The birds will cling and feed, a bit of squabbling btwn species but that is OK.