Yep. I saw a demo and was amazed how easy a center-punch would break a side window. The nice thing about it was that you didn't even have to whack it real hard. In the demo it just took a medium tap with a little pressure. I figure that would come in handy if you were injured or in a strange position and couldn't get a full swing. It is supposed to be even easier underwater with the pressure of the water helping to break the glass (the same pressure that makes it very hard to open doors until your car fills up).
I figure it would also come in handy if I had to use it to break somebody else's window after coming upon an accident.
I guess the trick is to store it in a convenient place where it would most likely stay put in an accident so you could find it quick, yet not be enclosed in a space that you might not be able to open due to damage to the car (like a glove box). I clipped a pretty sturdy sheath for it next to my car seat and hope that it will be there waiting if I ever need it (knock on wood).
Great thinking. If a car is underwater and pressure from the outside, per your post, I would suspect the entire window would break up into tiny pieces of glass. What would happen in your case of coming onto an accident on a road? Would the center punch break the entire window or just part of it? If it doesn’t what do you do? I’m also thinking of how not to spray a passenger with pieces of glass.