I worked in shelters and as an ACO and have seen too many awful things relating to collars - regular, flea and breakaway. Remember getting a call from a frantic woman whose cat had tried to get a collar off and managed to get it stuck in her mouth. The cat was terrified, running blind, hyperventilating, and the woman was afraid of her so she called the police for help. I was finally able to capture the poor kitty and had to cut the damned thing off. That cat was lucky someone was there but many are not. Had she been outside and/ or alone, the outcome would have been very different. It's also not uncommon for a cat to get a front leg stuck in a collar and if it's not discovered and removed in time, will cut into the armpit resulting in infection or worse if it's a flea collar full of pesticides. Any collar, including breakaways, can become embedded or be a choking/ hanging hazard.
I know collars w/ tags are important to help ID lost/ found animals but truly despise them on cats. Even our dogs don't wear them unless they're going somewhere. I remember a case about two family dogs playing in their fenced yard. One got his leg caught in the other dog's collar and their panic increased as the collar kept twisting and tightening. One suffocated and died; the other needed to have his leg amputated.
If a cat must wear something for identification purposes, make a paper collar, preferably with perforations, and write contact info on it. For flea control, use an oral or a safe topical like Advantage dosed appropriately.