adroll is more of an open ad marketplace, a site can be in multiple rolls and from what I can tell the sales force isn't actively pushing individual rolls. It also doesn't appear to be very selective. The CPMs are pretty bad compared to what I would expect with a niche network and a good sales team.
If you want to advertise on Surfing sites would you rather go to the surfing roll at adroll or to a niche network focused on Surfing sites that has the best sites and good ad placements?
Playing around with adroll I also noticed that once you want to advertise you still choose sites individually where in a network you are usually paying for the expertise of the network builder to have chosen the best sites.