The first and most important thing to remember is that the trackers DO NOT replace microchips. They do not provide permanent identification for your pet. They should be used in conjunction with a microchip. Their main purpose is to track your pet's location, not to provide identification for your pet if someone else finds it.
There are several different brands and types of this product, but they all have a similar style. All of the products we found consisted of a device that attaches to the pet's collar plus a separate tracking system, either a specific handheld system or an app on a smartphone or computer. An important thing to note is that if your pet loses its collar or the battery runs out while it has escaped, there won't be anything to track. If your pet is famous for losing its collar when it escapes, this might not be a good option. Also, compare battery life between different brands when you're researching.
We did find a comparison from ConsumerReports.org that tested three of the GPS systems, including the most popular (or most advertised) system, the Tagg system. You can see the comparison report here.
The other thing to consider is cost. The prices can range from around $100 to $500 or more, depending on the type of product, plus you may need to pay extra charges to continue membership or subscription services.
The key thing to do is to research which type of system would be best for you. If you have any questions about the systems, always call the manufacturer to get the full story, especially if the website isn't clear about subscription or membership fees. Also, check out reviews from other customers to see what their experiences have been. Sometimes they are the most effective way of finding the pitfalls of different products.
Good luck in your research, and if you have any questions, please give us a call!