Is that an F&S luggage rack though?
I looked at both links, this is the only seat that looks like it will fit with out modifying a stock bike. Regardless of what the other link says those seats with no passenger backrest definitely will not fit a stock bike without some sort of mod. The UK one appears correct and the write up says in so many words that you need a “US sissy bar”, which to me means it won’t fit the older bikes that may have the short back rest without swapping the rear. Look at these two pics to show the difference.