I've also been following threads on these collars and it seems that the majority of people who are having real success (instead of no change at best or fatality at worst) are those using them as training tools instead of just leaving them on. They're putting it on the roo when he's crowing but when he's been quiet for a while, removing it and only putting it back on if he starts up again. That means devoting A LOT of time to watching your roo to catch him in the act in order to "correct" his behavior.
I can't have roosters where I live. So, I don't have any of this drama and no experience with these collars but just thought I'd mention it.
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