OK my wife (50kg, 5' 9") has been on the back now. I haven't seen any pillion reviews so here is hers:
Right foot peg is basically in the exhaust flow - her foot is getting warm.
Seat feels like she'll slide off the back if not careful (I have always had racks or boxes on the back of other bikes - I have a rack on order).
She preferred the KTM Duke 390 but this is still better than the sportster or TW200. She's ok for short trips (which is what we do mostly - she's worked out that I can get her anywhere in Singapore - right up to the door - must faster than any other form of transport).