I have tried these nipples for 3 years and have only gotten frustrated trying to put them in the babies mouths. They are not firm enough to work with while teaching a kidd to take a bottle. I am throwing them away this year.
I keep Soay sheep which are a pretty small breed. Though they tend to be VERY good mothers, a couple of times I've been surprised suddenly with a tiny, squirming bottle baby. For such tiny little mouths, this is the only teat I've been able to get them to nurse on. I've never had problems with the little ball falling out when I wash them... perhaps I've just been lucky?