The accessory bag is a great addition for the Vest Pack 2.0! It has a snug fit between the water bottles; I honestly cannot tell that I added the accessory bag while out running. It's a great location for the important items that I wish to carry along, but do not need to reach for as frequently (for example, I store a mylar emergency blanket, hand warmers, and snacks during the winter while snowshoe running). Now that I have more room in my front pockets of the Vest Pack 2.0, I would consider adding smaller soft water bottles for ultra trail distances in the future. The accessory bag also allows extra space to carry items for my dog, when she accompanies me on a run.
**An additional positive comment of the vest pack 2.0, while snowshoeing... I have significantly less snow on my water bottles due to the "higher" location of the bottles on my back!