I am only familiar with these sorts of collars for dogs that are supposed to help with stress behavior issues.
I personally did not think that it made a significant change for the amount of money the darn thing cost me, it did however make me feel better that I had tried to do something for my old dog at a time when he was stressed.
My biggest query about these collars being unsafe for birds is...... exactly how close to the bird does this collar need to be to become unsafe? I am thinking if the collar is close enough to the bird to be unsafe then your cats are probably too close to your bird for your bird to be safe.
I am guessing that if the collar is on a cat and the bird can get close enough for the collar to be unsafe then my best guess is the bird is living in an unsafe environment in the first place as the cat can get close enough to be a significant danger to the bird. If you can work out the distance these collars need to be to not be a danger to a bird then you may find that they are not really a hazard at all. Like for instance, if a cat flea collar is dangerous for a bird and my old cat had of worn one I can guarantee that the collar would never have been an issue to my bird as my cat was never allowed close enough to my bird for the collar to have become a bird danger anyway.