I got two for my first two cats and I love them! They don't hang down the neck (where my one cat would bite at it and get her tooth stuck), so it also doesn't jingle. It doesn't add a bulk to it to where it's uncomfortable for the cats. I forget how much I paid for them, but I do remember looking around and finding these the most reasonable! There are different styles and sizes, so you can't go wrong!
Pros: Well designed and made, doesn't irritate cat
I bought a boomerang ID tag like this on Amazon, from the seller Leashboss, and I love it. The seller is easy to work with, and makes a great product. It was about $14, and worth every cent.
When we adopted Indy 4 months ago, he had never worn a collar (he was 3 1/2, and had lived his whole life at a cat rescue). Just getting him used to a collar was a struggle, and anything dangling from it (bell, ID tag) drove him nuts. But I wanted him to have ID on him, in case he ever gets out of the house. This ID tag was the perfect solution! He doesn't even know it's there, and it can easily be transferred to another collar when I rotate them -- which I plan to do monthly
Pros: I love that they don't hang down and add weight to my cat's neck, and jangle
They come in different styles and sizes for both locking adjustable and belt buckle style collars of different widths. In other words, you can thread them on a collar with an end or put them on a collar that doesn't have an end that is thin enough to thread it on. I found out about these on this site, got one, and love it! Good for cats or dogs!