Well basically if you compare that to let's say a piece of lettuce it "should" be better in terms of nutritional values.
But to be honest I'm personally not a huge fan of these products. I just prefer to eat my veggies not to substitute them with some weird green potions. I don't mind the taste and they bring volume to my diet (makes me fuller) without not that many extra calories.
haha.. the same arguement is given by the 'whey protein' kids that insist it is real food
a greens powder is heavily processed. processed foods are not something that will replace a whole food in anyway.. if that was true then by now we would only be consuming powdered everything