Loading up the Amalur demo gets you an armour set to be used in Mass Effect 3 as well as a couple of things for the full version of Amalur. If you complete the Amalur demo you get a gun for Mass Effect 3.
Playing the Mass Effect 3 demo gives you daggers for Amalur but the ME3 demo doesn't come out until valentines day which is the week after Amalur's release so a bit lame but eh it's a free item. Since KoA: Reckoning is a new IP it's a good way to get people to play the demo and learn about the game since a lot of people are excited for Mass Effect 3 and thus the free items may appeal to them