I agree with Doug. These things are tough as nails and designed to take the punishment dished out by the roadside including being run over. The more common version also uses 3v lithium batteries which are more likely to work after sitting in the trunk a couple of years than the competition.
As far as leaving something that expensive on the side of the road, that's what its for. If it prevents a semi from taking out my second biggest investment, then it was certainly worth it. I believe the more common breakdown situation for most folks will be to call AAA from the cell phone and wait rather than walking for assistance; thus, the potential for theft is minimal at best.
On a related topic, if you are on an interstate highway and unable to get more than say 10 feet off the white line, consider getting out of the vehicle and out of harm's way. Your chances of getting hit from behind by an errant driver may be much greater than the limited safety the car provides from the roving criminal element.
Craig.