It will be around 20 seconds faster to remove the AeroPack Trunk Top Bag from the bike, and it will be easier to carry (good for commuting, quick cafe stops etc) The full integrated AeroPack Carbon and Alloy S & X are lighter than the Rack + AeroPack Trunk Top Bags in the X & S Series If you have an X or S Series rack you are able to carry gear on top of the rack, when the AeroPack Trunk Top Bag is not present. If yes, the X Series Pannier Racks or S Series Trunk Racks with the detachable AeroPack Trunk Top Bag is the right choice for you. You can buy these together as a set, from the X Series Rack & Bag page, or S Series Rack & Bag page. If no, it is not important for you, then either the AeroPack X or AeroPack S will be the right choice for your needs.