I've got one of these, but under their previous name, Loca8tor.
Don't buy replacement batteries from the company, buy them in bulk off Amazon. Much more economical.
You can train your cat to come home by switching on the receiver, which makes their collar bleep, and giving them a treat. Like the Pavlov's Dog training.
It's proved invaluable, one night, when there was a massive gale on, MCat didn't come home past his curfew. DH and I wandered about, with the receiver, heard his collar bleep, called him and he jumped into DH's arms. He wasn't far from the house, but the gale had obviously scared/disorientated him, and he was hunkered down, too frightened to even answer us with a miaow.
I'd love to get a real time GPS for the boys, but the collar tag is so big and bulky.
If you do decide to put a device on your cat, please use a quick release snap off collar, the elastic ones can cause horrific injuries and death. If they lose their collar, you'll most likely find it with the Tabcat receiver, or you can buy replacements for about £25.
Shame microchips can't be used in the same way, but there's the problem of what to do about the battery.
But yes, I'd definitely recommend the TabCat. even though people look at you like you're mad, spinning slowly in circles, pointing what looks like a credit card