I got this to complement my car emergency kit. It is very solid and could do much more than those emergency window breakers, such as pry the doors/boot/engine compartment open if needed. At the price that it is it is a real bargain. And has many other uses as well.
The steel doesn't look as if it is of the best quality, so keep it as dry as you can so it doesn't rust. And perhaps keep it out of plain site as it is probably a car thief's car-key - for your car!
If you do buy it along for your car, I suggest you also get a complementary seat belt cutter just in case and keep them at close reach from the driver's seat.