When I bought my K1300s in 2014, it was clear my wife would not ride on the back without a backrest, and considering the accelration involved, it seemed a good idea. My wife was only 4'11", and she couldn't see much of the road in front of me. Consequently she had no clue when I was about to really nail it, and she was afraid she'd go right off the back.
We both also were instantly uncomfortable on the stock seat. It slopes forward a bit, and that was very uncomfortable on my balls when stopping, and any stops with a passenger had them sliding into me.
Since I was coming from a 1985 K100RS with Corbin seat, I was very interested in replacing the stock K1300 seat. I bought the K100rs new in 1985, by the way, and had been riding it for 30 years.
After checking various seat vendors, and not liking the looks of most, I settled on buying a new Corbin, mostly because it was the only one I could find with a rear heated seat option.
With the new seat, plus Corbin backrest, the forward sliding was mostly gone, the heating elements were a godsend in cold weather, and the backrest made my wife feel much more comfortable and safe. I do feel that the seat is hard, which I expected as the old one was firm too, but the new one seems a bit harder. I probably should have requested a slight increase in the padding level, but then again I don't ride enough anymore to avoid saddlesores on any seat.