RB is right on.... 1 thru 7 all true.
Third party, poor coverage and a real pain to deal with. "hold off we have to send an inspector out" Customer PO'd...car has to sit at least 24hrs.
As a service advisor the most common customer statement made to me...
"but the salesman told me "everything" is covered bumper to bumper.... NOT."
Don't buy from the sales person alone, see the finance guy. He's usually the one at the dealership responsible for extended warranties.
Even GMPP, which has about the most comprehensive coverage has exclusions. Like the bumpers themselves, glass,trim,serpintine belts,batteries,etc,etc.