I hear what you are saying WPC80, but the decision I made to have one fitted was swayed by two factors. Firstly I got a hefty discount on my insurance for having one of these devices fitted and secondly, unless you have gap insurance (about the same price as the lifetime subscription), you will never get all the money back you spent on the vehicle if it is written off. The discount on the insurance is annual, so within a few years, you will have paid for the tracker and after that it will save you money.
Vehicles with trackers fitted don't advertise the fact one is fitted, in case the theif finds it or 'jams' it.
It ain't foolproof but it helps me sleep at night!
You pays your money, you takes your chance.