a hidden kill switch or two would go a lot farther to helping you keep your car than one of those- the lock might keep the low level people from getting your car, but anyone with any experience in stealing cars will be able to get around it in a short time.. hidden kill switches will take too long to find and bypass and the thief will give up and move on to an easier target.
in both cases, there will likely be damage to the car, but with the kill switches you will still have the car..