Whatever you buy - GM or off brand, be sure it is through the dealership. GM will honor those.
My wife bought the Off-Brand bumper to bumper extended on her certified used '11 Buick Enclave in 2013, through the dealership at time of purchase. It was $1200 or something at the time. It paid for itself 10x's over. We are 2 months from the end of the warranty and the alternator took a shit 2 weeks ago and melted a wiring harness and blew a ton of fuses etc. The car would have went to the junkyard after that little electrical fire. It was Schumacher Chevy near us that did the work. They honored the warranty; we didn't pay a cent; and had the car back in 4 days.
With all these newer vehicles getting so deeply integrated with the electronics, its not worth taking a chance. I plan on buying one for my new Burb soon.