We had Holly chipped when she had her second vaccination with the vet.
She yelped like I have never heard before. It wasn't very nice to listen too, but I got the nurse to hold her while they did it.

It was over and done with in seconds.

I think if it increases the chances of them being returned to you if they get lost then it is worth it. I would devastated if Holly went missing or lost.

For the cost of it (cost us about £16) I think it is well worth it.