My wife is not your typical wife passenger. She has her bike, a 1985 Yamaha RZ350 Kenny Roberts replica. So she's used to riding sport bikes and knows how to ride front or back.
If not on the back of the Valkyrie, she would be on the back of this. This was a couple months ago at Deal's Gap.
She likes the comfort of the Valkyrie and had no problems with riding 600 miles while wearing the backpack. Although she said next time she'll not pack as much.
No marks from the tank bag. I think the key is to make sure it's clean before you put it on the tank and don't slide it around. lift it straight off and put it straight on. When the tank bag is not on the bike, don't lay it down somewhere that it can pick up dirt or other debris...of course nothing metal.