I've got the racks you're asking about (I use em with Givis, though).
They are fine for street and gravel roads, but I wouldn't want to trust them when it comoes to single track and terrain that would be pretty much warrant falling over . . . . .
"Here is your country. Cherish these natural wonders, cherish the natural resources, cherish the history and romance as a sacred heritage, for your children and your children's children. Do not let selfish men or greedy interests skin your country of its beauty, its riches or its romance.” T.R.