We got one with our R1T....it is currently hanging on the key holder in the house...never used it. I have the keycard and use the Paak (Phone as a Key) to control everything on the car.
Definitely get the fob. It is the only "key" that works if the bluetooth module in the driver door handle goes out (yes, that is where that it). If goes out, can't unlock door with card, can't hold car up to interior of door to start, and can't use phone at all to start the car. That happened to us and all key cars and PAAK will not work if/when that happens, but fob will usually still work as uses a different transmitter. It's a good backup, but I just carry it with me always as the primary now anyways.
You can get one from the service center. I did it recently on a R1T I purchased that didn’t come with one. It was $175 for the fob and $60 for programming.