In reply to Ben_Climber:
> Others have also said not to bother as if it gets stolen it is covered on insurance.
Not owning a car, I'm not very familiar with car insurance. But I'm going to guess that if your car gets stolen, your insurance premium will go up. And you may not get a replacement car that is as good as your current. And you will have a lot of hassle. Admittedly, recovering a stolen car probably won't be trouble-free...
So, if you can add a cheap tracker that might lead to the recovery of your car, then it might be worth it.
The one thing I'd suggest you need to be aware of is the battery drain. Assuming you want the device powered when the car is parked. Even though the power it takes is pretty low, it is still a load on the battery, and, if left idle for a long time, could flatten your battery.
You also need to find somewhere to conceal the tracker where it can still see the sky (satellites), and communicate via GSM. I've seen plastic bumper voids suggested, but I think you'd need fairly good waterproofing for that location.