Well comparing a regular MMO to a voxel base game really can't be done. No Man Sky is in competition with games like Star Citizen and Elite dangerous. Dual Unvierse is in another world. Dual Universe is in the Space Engineers world but Dual Universe will have a chance to be in competition with voxel base games and the normal space sim world if it's done right. I never understood the hype around NO man SKys but everyone finds different types of games entertaining.
If you were going to try to compare these two games then after playing a week of a voxel base game like Dual Universe then more than likely you won't ever pick up No Man skys again. lol After you play a voxel base game like Dual Universe then your average space sim like a No man Sky becomes extremely boring.
You're comparing a Space Sim which is your typical Exploring a Universe fighting and trading VS the Sci fi voxel base sandbox games which has Building your own ships, bases and planet, trading, fighting and exploring plus traveling on a multicrew ship with friends that you've built?. I mean the choice is obvious. I'm still on the fence about the combat system but Dual Universe could be the game that ends games like No Man Skys.