I bought a suet feeder last year. Early on, a woodpecker and a Flicker visited it, understood how to hang on, and apparently liked what they found inside.
Unfortunately, they didn't return. Just moved on, I guess.
At first, when I saw that a suet cake seemed to be showing its age, I sometimes replaced it and just dropped the old one on the ground. Several types of black birds, like Common Grackles, Red-winged Blackbirds, and European Starlings (plus squirrels) would peck away at it down there. (Squirrels can’t get at the feeder due to a baffle.)
I sometimes wondered if my suet feeder was worth the effort.
More recently, however, I’ve been leaving the partially-eaten cake in the feeder and, since there’s room, actually inserting a second cake.
This year, several species have figured out how to hang onto this vertical contraption and enjoy some greasy goodness. I’ve seen all of these visitors hanging around: Downy Woodpecker, European Starling, House Sparrow, Red-bellied Woodpecker, White-breasted Nuthatch, and maybe one or two others I’ve forgotten.
So I guess my purchase wasn’t for naught after all.