I have a set of gray ones I used for a while but found I wasn't really in love with them. For me, the concern is that since there is no zipper or "bag closure" (like on the Carradice saddlebags) to close before closing the flap, dust from dirt trails gets inside. Also, their shape is not really laptop friendly.
Still, they held very well to the rack and bike, didn't sway and didn't cause any problems. I still have them and will probably plan on giving them another try, possibly on the Betty.
René