I bought one for my cat, never did help with finding him, just the general area.
They're not great for tracking things that move on their own, or things that avoid people.
we have them for our cats, they're great. Sometimes they're hiding in bushes and we don't realize they're 10 ft away. Other times they're down by the neighbor's house. It's not perfect but it tells us which direction more or less. And definitely more peace of mind if they ever got lost. They
They make breakaway collars so if they get caught on something it won't trap them.
We use them on our cats and have found the trouble-maker cat 3 times out of 3 when needed (in an urban apartment area; most recently the cat was scared by a noise which may have kept her hidden out all night in the cold, unless we had found her/shooed her back to the house)