I cant really speak about the dual sports bc I havent ridden one. But, I do own a Marlin 5. I bought it so I could ease back into single track riding with my son. I have actually put more road miles on it than anything though. Gravel, bike path, road, etc. I view it as more of my 'go anywhere' fitness bike now.
anyways... it is a solid choice, in my opinion.
Edit: I do have an older 7.3fx that is now dedicated to my trainer. Not really a dual sport... but it is a hybrid.