I am not familiar with xzilon, but I can tell you what I know about Lo Jack. I am a police officer in a small city in South Carolina. We have recently gotten a Lo Jack system. This system puts out an audible sound when a patrol car is in the vicinity of a stolen vehicle equipped with Lo Jack. This is a great tool for us.
Here are a few things to consider:
What is the vehicle theft rate where you live? If you're in a high crime area, this may be more beneficial than in an upscale gated neighborhood.
Also, check with your local police department to see if they have Lo Jack equipped vehicles. It does you no good to spend the extra money to put a Lo Jack system on your vehicle if your police department cannot track them. Call the local police and ask for a vehicle theft investigator. They should be able to tell you about the department's capabilities. And will be happy to talk to you.
Finally, consider how much you travel to large cities. If you travel a lot, this may be a good option.
Hope this helps.
Michelle