Answer: iPad makes for a great gps device. Too great. There are too many features to keep your eyes attached to it, rather than on the road.
A vehicle gps has limited options and is fairly basic. You don't have all these neat features to play around with.
And now this user texts while driving because he, by law, can't talk on the phone while driving??? Wow.
Either way, do as you wish.
I think you might have made an assumption about GPS apps for iOS. As for GPS on the iPad, it's really not much different than on the iPhone. The apps I use on my iPhone are just about identical to what you would see in a stand-alone GPS unit (e.g., TomTom), or built-in automobile GPS. They are very uncluttered.
I primarily rely on voice guidance, but if I do need to look at the screen I would think the iPad would only make that easier as it is so large. So I guess I don't see why it would be more dangerous than any other GPS options out there. I see tons of people with 3"-3.5" GPS units stuck to the windshield. Surely looking at that is worse than looking at a well-placed iPad screen.
As for the texting while driving remark, I kind of hoped that was in jest. After-all, in no state of the USA is cell phone use prohibited whereas texting is not. In fact more states prohibit texting while driving than talking on a handheld. And no states ban cell use outright, only for certain youth drivers and/or require hands-free operation.
Michael