Seems to me a little empirical testing is in order... if it has trouble
getting the fix on the dash, what happens if you move it to the side
window?  Then try it in someone else's vehicle, which doesnt have that
heating grid.

Doesnt matter, then, what experiences others have had.

If it then locks in, seems to answer the question, and you can take it up
with the product mfr.... though from my long-ago background in RF
propagation, I wouldnt be at all surprised.

Why don't you try the sat nav outside of the car.

If it has the ultra thin copper sheet in the windscreen, that's probably it. I
once had a Ford Taurus with that type of windshield and had to go to a remote
mount radar detector to get more a few hundred feet detection range.

Satellite nav has a hard time getting through a-thermic windscreens.  
You need to use an external antenna if there is a connection for one, or
one of the new SiRf III chipped gps units.

Also try asking your questions here:

alt.satellite.gps

or

sci.geo.satellite-nav