My animals are microchipped but I'm not a fan of them since I had a less than positive experience.
I got Molly chipped when I had her at 8 weeks. Fast forward to when she was a year old .... I took her to the vet to get her booster shots done, then they scanned her to make sure her chip was ok. They couldn't actually find it, so the vet tried with another scanner. They tried I think 3 or 4 different scanners including a hand held one. 3 people tried to find the chip and couldn't. They recommended I take her to a different practice and try it there. I did, had different scanners and different people and they still couldn't find the chip. They were scanning the whole of her incase it had migrated.
The assumption was the chip had fallen out not longer after it was put in which is apparently possible. After doing some research of my own it could also be that the chip failed.
I can't help to think what would have happened if she had gone missing during that year .. they would have be looking for an animal that was chipped. I just don't trust them any more and would never put 100% faith in them.
I was quite mad when I found out - they re-chipped her free of charge. Now I have a problem that Molly is petrified of the scanners