I have a bubble collar that I used on Reggie but he could get around it. I doubled it up with other collars, like a leather collar below it to cover his shoulders and to stop him from getting below his shoulders. It stretches the neck out a bit. It's pretty easy to use if you have a bird that's easy to handle. I can take pictures of it for you if you want but basically, it just two pieces of plastic that snap together. If you can't handle the bird you want to put it on really well, you're going to have a hard time getting it on said bird. I would cry if I had to put this on one of my greys. You would also want to use it in conjunction with some collar that will cover the shoulders or it's probably not going to help. And if you can't find a solution to the plucking, ultimately, it's probably not going to solve the problem anyway. Reggie had zinc poisoning and ultimately pulled all his feathers out and now he's mostly naked. We chelated three times and just couldn't get the zinc levels to ultimately come down low enough. Chelation is very hard on the body and we didn't want to keep going. This was about eight or nine years ago and I had him retested about two years ago and it was still high but had dropped some more. Chronic zinc toxicity is a really hard thing to deal with. I would definitely test for metal toxicity on a picking bird if you haven't already.
