
HD...........You're responding to a quite old post from about 3 1/2 years ago or more. I did in fact purchase a Mustang seat with the back rest as you and others have mentioned. You're quite right in that it is easy in and out. Problem to me was it was TOO easy to move and hold the selected position (up and down). Those "detents" are not deep enough to keep the back rest from sliding down below where ya had it, if you apply any pressure to it while dismounting.
So, being as clever as I am, I decided to tighten up the "set screw" that goes into the "detent". Quickly discovered that it was NOT quite the kind of setscrew arrangement I had expected. I thought the hole thru the backrest brkt was threaded and the nut around the setscrew acted as a "locknut"...........

Nope, the nut was tacked to the chrome backrest brkt, and I easily broke it off thinking it was riding freely on the threads of the screw itself.
Soon after this incident, came the M. Beach Bike Rally and Mustang Seat Company was there. They "warranted" the set screw problem I had and the guy said I was the second one with the same problem that he met up with on the same day. Furthermore, that he had worked for Mustang for over 10 years and never had seen that problem before. At the time it occurred I was well beyond a normal warranty period...........so hats off to Mustang for helping me out.
have since sold the bike and now considering if I want to get a custom seat of some sort for my new Street Glide Special. (2014).