Whereas I fitted one on both my cats when we first got them and got a great deal of reassurance from it. Yes its range is pretty hopeless but it does give you the ability to move around and check other people's gardens and common areas in the event that a kitty does go missing. One time after Milly was missing for hours we even managed to locate her to under the utility room work surface
She had snuck in by the side of the washing machine when the cupboard door was open and had sat quiet as a mouse in there ever since. Quite often too we would call Milly in and she wouldn't come, so we'd get the tracker out and discover that she was hiding under a bush about 6ft from the back door
Eventually I dropped the base unit and broke it and as the kits were well established here by then, I haven't replaced it. If they find a way to make the tags smaller over the next few years though I might consider it again!