They are pretty different. Check out skiphop.com for descriptions and dimensions. The Dash is more of a messenger style with a flap that comes over the front. It is wider than it is tall. The Duo is taller than it is wide and has an open top (there is a velcro closure, but only in the middle, so things can still fall out). The Duo is an odd shape and stuff really gets lost in the bottom - you have to dig to get stuff out of the bottom. But those large front pockets and the side bottle pocket are great drink holders when the Duo is attached to your stroller!
They look the same but a $25 [price difference)
