Works for any type of collars.
Well, I know it is not a good idea to feed your bird on your shoulder when you are in the nice clothes though your bird is in a nappy suit, because your bird spreads the seeds all over your clothes while eating. However just out of curiosity I tested the mobile bird feeder on different clothes with the different type of collar. As you see it in the image it actually worked. I needed to use a mannequin to take a proper photo but my bird Charlie enjoyed eating on them. The feeder stayed there firmly.
I usually wear T-shirt to go out with my bird and let him eat on my shoulder, but there you go, my experiment proved you can wear any type of clothes to feed your bird with the mobile bird feeder!