I got loc8tors for my two boys when we moved house earlier this year - since you can buy a set with the box and two tracker tags I just needed the one set and it covered both cats; if you've just got the one cat then it can be a spare. I fitted the tags on breakaway collars - the snap types, not elastic, since elastic collars can get legs tangled in them and cause injuries.
The tags are small and weren't any bother for the cats to wear, and they did work - to a certain degree. I live in a reasonably built up residential area with lots of fences and sheds and hedges, and unfortunately the radio signal just doesn't go very far through objects like that. When the cats were a garden or two away then the tracker would show they were nearby and in which direction, but most of the time when they were outside I'd get no signal on them. I tested the tags when I got them and a tag tucked down under the edge of a hedge around the side of the house wasn't showing up from the pavement when I tried searching.
That said, the first day I let them out, after a few hours I tried tracking and in the front garden I got a hit which showed a cat had gone over the road into the nursery grounds - I walked over there and came across him lurking in the undergrowth. I wouldn't have searched there without the tracker showing his general locations. And early on one came back without his collar and I walked around the block and got "a hit" in the cul de sac backing on to my back garden - where I came across the lost collar and tag in a hedge. And a few times when it's dark and I've called for a cat but not heard any meow of response, I've tried the tracker and got a distant beep which indicates that the tag's owner is either quietly trotting back home or is skulking in a garden nearby, which was reassuring.
However in the first couple of months after letting them out, I've lost 3/4 tags without recovering them - I bought a replacement set of two tags early on so had four to play with. Monty still has his tag as he was less prone to mislaying collars, but Rolo's got through three of the buggers. I've done plenty of wandering around the neighbourhood with the tracker but got no signal; and I even started adding a disc with name and address in the hope people would find them in their gardens and return them, but nada! A typical collar loss would probably be it getting stuck at the bottom of a hedge or somewhere else like that out of the way, and if it was behind a plant pot or a shed or something in a back garden, you'd have to be only 10 metres or so away to get a hit on it I reckon.
It's a shame it can't have a stronger signal to overcome the built up area interference as I think the idea of the product is sound, and I did find it reassuring at various points, but I won't be buying any more tags - it gets quite pricey quite quickly!