I bought this feeder because I liked the color.
Finches and other small birds seem to enjoy it.
Black sunflower seeds (not the big ones with white stripes) fit in, stay in and the birds are able to get to it without trouble.
Collapses flat for easy storage.
The seed hasn't lasted long enough but I think with air and drainage, spoilage won't be an issue.
I have only had it for two weeks but the sunflower graphic is a sticker and will most likely fade over time. (not a real con, just an observation)
Perch Birds - I have seen any. Robins have been below the feeder as well as doves. I was hoping to see some cardinals; however, at this time they don't seem interested. I don't know how imporatant/effective the perch rings are. I also have a no/no ball feeder and the birds seem to enjoy them both equally.
I have a finch feeder next to this with thistle (nyjer seed); however, the early spring finches and warblers seem to prefer this feeder / black sunflower seeds.
I wouldn't add a mix as I think it would just fall out. Since I see robins and doves below the feeder, I assume some seed falls out (but most likely it is caused by the birds).
Filling this is not difficult as the cap slides open. I have no squirrels to worry about so haven't had to worry about what those fun little creatures would do to it.
Overall, I am happy with the feeder and would buy again. If you want to feed small song birds and to keep larger birds at bay, this is a good feeder. If you want a large mix of birds, this will discurage the larger species.