I have had Mustang seats on several Road Kings and chose Mustang again for my SESG. I use the solo w/rider backrest and have two pillions. I use the 8.5" when riding solo to keep the low, stock look and the 13.5" when riding with the bride. Changing them is a two minute operation. Mustang makes several other good choices, some for taller riders.
I find the Mustang's rider backrest to be easily and widely adjustable while riding. And, Mustang's quality, delivery and customer service is excellent. Many report problems dealing with Corbin from afar. Though I've never had to do it, Mustang will exchange or refund a seat if you don't like it. (If you buy directly from them.) I don't believe this is true of other manufacturers.
You'll find passionate supporters of Corbin, Mustang and C&C on this forum.
I've posted elsewhere on the forum, but to make it easy, I've included two photos with this thread. One with the 13.5" pillion and one with the 8.5". Hopefully, the administrator can combine the photos into a single post.