I have first hand experience with one such device. From a technical standpoint (and avoiding the shopping aspect of the question) most of the options seem to deliver similar features and performance.
We live in a house by the edge of town, and we're surrounded by meadows and forest. That should have been a clear sign for me that the collar wouldn't be a great idea: the GPS trackers are fairly bulky, and they stick out quite a bit from the fur. When Max, our cat, came back home for the first time without his tracker, I had to go fetch it. It took a long time to get somewhere in the middle of the woods, and as the device is accurate only to about 6ft it was hard to find under brushes and branches. The same thing happened 3 times, until we finally decided not to fit it anymore, and sell it off.