This is going to sound very negative, I am not a great believer in them, I am just trying to portray all the aspects I have thought about over my 20 years of driving/owning/insuring.
For clarity, I do have one, on my Ducati (Bike Trac from Road Angel) and I also work at a large motor insurance company :)
Your insurance usually give you zero discount for a tracker, assuming you get a Thatcham approved one (cat 6 or 7) fitted by an approved supplier of course. The only one that I know of that does definitely give you a discount is a telematics device so that the insurance company can monitor your driving style and speed etc 24/7...
You get a discount on your insurance for having a piece of security - for my motorbike for instance, adding a lock gave me a discount, having a ground anchor gave me no more discount, nor did a chain nor would adding a tracker to the cost, all it would do is make my bike less likely to be stolen than the one next to it and you can't go putting a sticker on your bike that says it has a tracker on it, it would be found and removed in minutes - even on a car there is only so many places you can hide one and it still get a GPS location - not to mention they can buy a device from some place in China that blocks the phone and GPS signal for literally about £50...
Then you have the next dilemma, if you get an eBay china special, are you looking at tracking down the crims yourself ? - because on the insurance approved ones, the second you report it stolen to the company (Road Angel for example) they will switch off your ability to see the location on the web site and only deal with the police directly so being able to see the location of your car is only useful if you forget where you left it when its not stolen. I am not sure how co-operative what little police force we have that cares about some stolen car would be with a DIY fitted device TBH. They also don't work under ground or say for instance in a multistory - cat 7 may do, I am not entirely sure (it has GPS and RF from memory vs cat 6 which is solely GPS based) - which is often the type of place they will leave them for a couple of days if they suspect it has a tracker (to see if someone picks it up). I consider myself fairly ballsy, but to wonder up to some lock up in a rough part of Bristol and demand my car back from some known car thieves would be beyond my personal comfort zone...
The other part of the argument is do you want your car back after some scrote has ranted the testicles off it from cold, bounced it over speed humps or god knows what when you get it back from being recovered...or would you rather it never be seen again and you get another car that hasn't? It's a tough one I know, we get attached to our motors, but I have seen it so often with mates and family who have a minor smash or their car broken into who sell it not long afterwards because they no longer feel the same about it.
If it will give you piece of mind then there is no price you can put on that. But if you think it is going to be a magic bullet to car theft then I think you are mistaken, otherwise they would fitted as standard to everything by now considering how cheap the tech involved is to integrate at manufacture.
The cost will almost always negate any likely premium discounts of the right kit - £300 - £400 for the first year with fitting followed by an annual sub.
