ah the dreaded brake nonsense again! one guy CLAIMED to have this ONE issue and it spread all over the internet in various places so I did some research and found that EVERY POST could be traced back to this web site.
There were no NHSTA reports on this even though I gave the web site out to him. IMHO he bought the car and didn't like it so was trying to get out of it.
quite simply the brakes in our cars, just like in other cars are HYDRAULIC and the only way they could stop working is with a total failure of both the primary and secondary master cyl ports. could it happen, maybe but I bet you could get million to one odds of that happening in Vegas.
could the POWER ASSIST stop working requiring more pressure on the pedal to stop the car? yes but IT WOULD STILL STOP. could the electric brake assist fail YES BUT IT WOULD STILL STOP!
I have a 2008 Yukon with 29K on it and it has had one issue with a faulty crimp in the wiring harness in the trans which caused the engine to shut off. it happened twice BUT THE CAR STILL STOPPED it just took a little more effort.
caveat emptor but this is one of the better new technology cars I have had and I sold a mercedes ml55 AMG and replaced it with this never looking back. I have owned multiple range rovers as well great off road but slow as an old dog on the highway.
good luck with your decision but I am totally pleased with my yukon