Can I ask why you want an in-dash GPS? From what I can tell from others I've seen they are inferior to say a Garmin 760/770/780 unit.
The advantages I can see...
Audio directly to the speakers via the head unit (Which, you end up turning off anyway.)
Disadvantages I noticed.
-Very large initial cost (as opposed to 250-400 for a good stand alone)
-Poor mapping compared to stand alone
-Difficult-impossible for simple system updates
-Costly map updates compared to stand alone
-Not at all portable, so locked to 1 vehicle/purpose
Also, you have to leave it in there - which is a large investment waiting to be ganked. Portable can be removed daily/easily and w/o any markings with the friction mount.
Just curious, as *I* don't see the in-dash types being anything worth what they cost for true GPS purposes. If you just want something that looks cool, that's something different.