how hard to install?

If you can find 12v plus and minus (battery or elsewhere always on) that's it.

thanks. just ordered two boots

So, if you have one of these, are the police willing to use it to make an arrest, or do you need to steal the cart back yourself?

I guess you would have to ask the police that question and they could answer that for you. :D However using a bit of logic I would think that if you know the location of a $15,000+ item you own that you have reported stolen I would think the police would want to go after the perpetrators if you could show them on a map where it is sitting. If you knew the location of your reported stolen car would they go, or your stolen jewelry? I would think your insurance company would also be interested.