I've had this tablet for over half a year. To answer some of your questions:
Yes, it does make a very good GPS for the car. I took this on our family road trip from Southern California > Vegas > Grand Canyon and it worked very well with FreeNav USA. The 7" form factor means it still fits in your pocket and the kids can hold it easily.
Samsung has promised that they will upgrade this to Jelly Bean 4.1. You can upgrade it yourself with unofficial builds.
The screen is great and I've rarely seen it chug except with intensive 3d games though I'd liken that to buying a regular laptop and expecting it to play the latest Call of Duty.
What no-one has mentioned is that this tablet has an IR blaster. This means that you can control your satellite/cable box with the built-in (and frequently updated) app. Very few, if any other, tablets have this.