Dude- I've been using a Nelson-Rigg magnetic tank bag, almost daily for three years. And I love it.. The only thing I would have different is I would get the one that expands to 9 inchs high.. Mine is the 5 incher

But, really.. the thing doesn't slide around much, (it's been tested at over 100mph a few times ) and doesn't scratch my tank. But make sure to keep it off of that little hump/vent thing on the front of tank, or you will spend an afternoon buffing out the light scratchs.. (don't ask me how I know )