Great for packing more stuff along on trips!
Bought a roof bag for the roof rack on my mini van when we were planning a week long family vacation with our four kids. Worked out wonderfully well! Take their advice and lay it out on your floor to plan what luggage/items will go where once it is installed. Did reduce our gas mileage a bit, and had some wind noise, but was a lifesaver to get everything we needed along with us. Came shipped fast, well packed, and with everything with it that was needed. Had thought about getting a hard sided one, but didn't have a place to store it. We did encounter some rain on our trip, but our belongings stayed dry in the roof bag.