I wouldn't use it.
My mother went through my things, my bedroom, my journals, notebooks, etc. all the time when I was a child.
Now I'm 22, and I recently found out she's been taking my cell phone when she has the chance to look through my text messages. I wouldn't be surprised if she logs on to my facebook or email, as well.
I've for the most part never lied to my parents, and the only times I did lie, I wasn't doing anything wrong or that I wasn't allowed to do, I just didn't want their freakin' nosy selves knowing everything about my life. I've never been in any kind of legal trouble, done any hard drugs or been a serious partier or had problems like that, I wasn't sexually active until after I turned 18, my friends were all seriously academically inclined, straight edge, also not sexually active. I'm sure if my mom could have installed a GPS in my car at that point, she would have. I don't think I realized how completely invasive of my privacy and untrusting she was until recently, because she never made any strict rules or gave me a hard time about where I was or who I was with. She's just NOSY.
I'd rather do something like check with other parents that someone will be supervising them, limit their ability to hang out with friends who I think are untrustworthy, etc. And hopefully by the time my kid is old enough to drive they're responsible enough not to do something stupid - and if they're not, well, good luck buying themselves a car and paying for gas.