Whether or not to use collars on cats is a bit of a dilemma. When I was a kid it seemed people always put collars on their cats, that was THE sign that they had a home and were cared for. A cat without a collar was a stray. Forty years on quite a lot has changed. One of the main changes is the introduction of microchipping. A chip is much more difficult to lose than a collar and holds the vital information (if kept properly updated) to reunite a lost cat with his or her family. There have also been some very nasty injuries to cats as a result of collars: Some collars can put cats at risk or being caught on branches etc. There have also been some horrible injuries as a result of a cat getting his arm through the collar. In the past I've seen cats of my own occasionally limp home wearing their collar like a shoulder bag. It's unpleasant but soon sorted out. However if that cat is straying/lost and gets into difficulties like this the collar can rub under their arm eventually creating some very nasty wounds, which without care can become infected.
It's tempting therefore to think that collars are a thing of the past and rely solely on microchips instead. The downside of this is that not everyone knows to check for a microchip if a cat is found, and not everyone can be bothered to try to catch the cat and take to a vet to be scanned. A collar can give this information more readily. In addition to this reflective collars can make the cat more visible at night and some people hope that a collar with a bell may do something towards protecting the local bird population. Personalised collars can also give out a clear message such as "do not feed" which could be very helpful if the cat is on a special diet.
At 8 Lives we've taken a middle line and use collars sometimes. Our elderly black cat wore one to increase visibility ... and because he had health issues and was underweight we wanted to signal that he had a home and wasn't a poor starved stray. Our younger rescue cats usually wear collars with our phone number on if they're allowed out. Our other resident don't. Some of this has to be about the cat's purrsonality. Our old lad never lost a collar in his life, whilst some cats are unable to keep a collar on more than a few days without losing it.
Whatever you decide is best for your cats, please make sure if they wear collars they're safety collars which will come off easily if your cat becomes caught on anything. Check out Kitty Collars for a lovely range of reflective and personalised collars. They've been very kind to us, supplying us with both personalised (with phone number) collars for our foster cats, and collars to sell for funds. They're lovely colours, soft or reflective, and can be personalised to carry your message. Marla, the lady who's company it is is lovely, very supportive of rescue and helpful.