I tried with a Araucana cockerel for about a month or so and either it was too loose to affect his crowing or so tight that he pecked and clawed at it till it became loose. I ended up feeling so bad about I took it off, the neighbours complained and now I don't have a rooster

That said I don't claim it could never work, I've seen convincing videos on youtube, also seen an advocate admit in the comments section it worked for 6 months then the rooster strangled himself trying to scratch the collar off on a fence post. I'm hoping to try again with the son of my last rooster since he has a calmer temperament and I've hand-raised him so I'm hoping for better results this time but not overly optimistic. Even it does work I'd be thinking of moving him to a farm after 12 months and trying with a new rooster since I wouldn't want to keep him in it his whole life. Maybe it gets easier if you think of it as a choice between near-certain death and the collar.
Another option might be bringing him in at night, keeping him in a box and not letting him out before 9am or some time you negotiate with the neighbours. A lot of neighbours will be less upset by a rooster crowing between 9-6 than one going off at 3 in the morning and you can definitely work for that. Keeping lights on the henhouse for a couple of hours and making sure it's light proof can also push back his crowing for a couple of hours. Maybe even a combination of these attempts plus keeping your neighbours informed and in fresh eggs can buy you some leeway while you try to find the right solution.