I like something more violent to the theif like an explosive device that takes out the bas@#$. But alas I'd kill myself some night when I forgot to disarm it. I think the battery device is great. You could make a lockable case to the battery that would cover the security tags on it. If they didn't see it and the car did run it would screw the thief up for a little while. Unfortunately all devices just slow the thieves down. For high investment rods, I like lojacks, because they will tow and hide your vehicle in a container. At least if you find it's missing quickly, you can notify the police to track it if they do lojack in your area, as they do here.
It would be alot easy to just cut the thieves hand off, like in China. Brutal, but effective( a bit sick tooo!)
Or better yet, tattoo thier face with their crimes. Make it harder for them to blend in!
Ultimately I like the hidden kill switch mingled with an alarm system to the car. The combination alerts you and slows them down a little. I met a guy years ago who sold these small battery operated motion sensor alarms. They don't conect to anything. They are about the size of a car alarm device on your key chain. and you activate and deactivate them with a similar remote. Since they are not wired to the car, cutting power does nothing. Since they are so small you can cram them anywhere. They also had built in motion detectors and a 110 deceble alarm. Pretty cool, cheep, and hard to locate, until they are screaming! Easy to throw away once found, but hopefully by then , your around to hear it! Best part is you can take it with you in rental cars, etc... Just one more thing to help slow them down!