Yup, there's no chance someone could slip the car in 1st or release the handbrake while having the starter armed. The only thing is that you have to think twice when leaving the car because if you forget something in it and disarm the alarm, as soon as you open a door or even the trunk the starter will not work any more.
I have it that way to make sure nothing ever happens. My g/f takes the car often, and we borrow each other's cars among my good friends so I'm better safe than sorry.
