We have the Bike Packers. Before we purchased them, everybody told us to get them instead of the rollers because they could still be closed when 100% full. We never heard any advantages of the rollers, but now that we are on the road we've thought of a few. The rollers are bug-proof. There is no way to complete seal up the packers from insects, so you have to keep food in sealed plastic bags if you don't want ants eating it. The other advantage to the rollers (if you are not carrying an additional dry bag) is that they can be used to wash clothes or carry water. You can't do that very well with the packers.
James
http://www.erck.org