I've had both....I used a Mustang seat with a backrest and now when buying the 2017 I am using the factory seat (modded by mean city cycles) and a harley backrest (guess I need to get around to selling the Mustang). Anyhow, I have been happy with both. My Mustang is not as adjustable (although it does have a bolt that moves it up or back) whereas the Harley one is fully adjustable. It's hard to predict how happy you would be with each as everyBODY is different.
One thing is for sure, I will ALWAYS have a backrest
2018 Road Glide Special. 12 inch 'Freedom' shield, Mustang seat, Harley tour pak, Advanblack lowers, Motolights, rear crash bars, Headset plug-in, Ciro footpegs, Black headlamp trim, mesh grill covers, Flash2open garage transmitter, buncha other stuff!!