I bought one though GIECO - it's $100 a year vice the $1500 the dealer wanted.
When some dirtbag broke one of my windows to get into my truck ... and get his ass chased across the parking lot by myself and two other guys ... GIECO covered the window. My comprehensive deduction is $500 but my mechanical insurance is only $50 deductible. When I called them they initially said they'd hook me up with their window service but the bill was on me. About an hour a later a supervisor reviewing the case called back and said that it would be just $50 because of the mechanical insurance.
Since I off-road the truck and have it customized I didn't want to argue with the dealer than the lift coils and skid plates caused this or that problem. I do all my own maintenance and don't need the arguments.