I am in a no rooster zone and for this reason do not personally have experience with the no crow collar as I do not want to try and push the limits and draw unwanted attention to my gals so stay within the regulations. However, I have researched it and have a friend who uses one on her rooster.
The collar does not work on all roosters.
It can take a couple of weeks of tweaking to get the right setting.
There is definitely a choking hazard.
My friend had a BCM rooster on who she trialed the collar and it took her probably 3 weeks to get it right and even then he still had to sleep in his darkened man cave with the collar on so that the neighbours could not hear him. She felt mean doing this and ended up finding him a home where he could crow to his heart’s delight. She did, however, keep one of his sons on who the collar does work enough that he can sleep with his gals on the roost and the neighbours cannot hear his crow attempts.
BUT she nearly lost her first rooster during the tweaking period, he started choking, got dizzy etc
If you are allowed to have roosters and just want to not wake the neighbours early, personally, I would prefer to trial a rooster coop which is darkened and insulated. That way he can still crow during the day, there is no risk of choking and early in the morning, everyone gets a sleep in