It's not a simple job to swap back and forth between single and dual seats. I have both set ups, (currently with the SDR single seat) and when I look at the dual seat parts hanging on the garage wall there are a lot of bits. Many times I've had the opportunity when a friend is staying over or something when they've asked to go for a ride pillion and all I can say that in three years I've never had the time or motivation to swap to the dual seat, it's too much trouble. Someone on the forum has designed a quick way to do it but they had to custom make quite a few bits.
My dual seat parts are not just the seat and rear side panels, there's an under tray, the duck- bill, the back light, the number plate hanger, the indicators, and a load of bolts and fixings. Also there are a load of other SDR parts that have to come off the bike before this would go on as well as the attachment method. It's just not that straight forward.