Hunter, the RangeTechnology Start/Stop device works with all GM vehicles. When I went to their website I went to the "Vehicles" drop-down and saw that my vehicle was not on the list. So I emailed them about it and one of their Customer Service Reps replied that the drop-down was only for the AFM Disabler (because that device prevents 6 & 8 cylinder cars from shutting down cylinders to save fuel). She assured me the Start/Stop device would work for my car (2019 Buick Regal Sportback), and sure enough she was right! If you are not sure then go ahead and email them - they responded to me within 24 hours.
I'm not 100% sure that all GM dealers will install the Auto Start/Stop device though. I asked my dealer and he said they would not install it (McKenney Chevrolet/Buick/GMC, Lowell, NC). We have bought 3 cars from them since 2008 and get regular service there, so I don't think he would lie to me. I can't speak for all GM dealers, I just know my dealer will not install it.