When I bought the 900 last fall, it only took five days to know that the stock seat had to go. I'd had a Mustang on the previous bike, so I expected a big improvement.
In that that first week, my wife and I went two-up on the stock seat and on the way home I literally had to drop her off (at her insistence) at a Target store to wait while I went home solo and returned for her in the car.
The next day I put on the Mustang and we went on a four-hour ride with no problems for her.
I've posted these photos once before, but for the benefit of those new to the forum and considering a Mustang, it helps to see the structural differences side by side.
(Drivers backrest removed for clarity.)
Especially significant for her was that the decorative studs on the OEM are aimed upward and she found herself most uncomfortable sitting on those metal studs. The Mustang gives a wider berth, and the studs are correctly placed on the SIDE of the seat, facing out not up, so as not to be sat upon. A major design flaw in the OEM seat!!