I have both books and use them both - I really like the quesadillas from Sneaky Chef and it seems other posters don't like the quesadillas from Deceptively Delicious.
One of the things I really liked about the Sneaky Chef was the ideas about a Breading Mix that I store in my freezer. It is an equal mixture of whole wheat bread crumbs (ww bread whirred up in the blender), wheat germ and ground almonds and a bit of seasoning. I use it to bread chicken fingers and make fish sticks. My boy really likes it. I don't know why I couldn't think up this myself as had been using white bread crumbs previously?
Sneaky Chef also has a flour substitute that uses equal parts white flour, ww flour and wheat germ. I also keep this in the freezer and use it in my recipes for pancakes, etc.
Sneaky Chef also has good ideas about making your own jello (which my boy loves) out of fruit juice and unflavored gelatin. My boy also loves the Breakfast Icecream he has as a snack - it isn't ice cream at all but rather frozen banana whirred up with plain yogurt, honey and some avocado for good measure.
But I do have to agree that the purees are all more "difficult" than DD in that they are puree-combos (sweet potato AND carrot for example). Another example is the pancakes in Sneaky Chef are made from 'scratch' rather than using a pancake mix like DD.
Not sure if that helps? I looked at them both before buying - I love cookbooks so I'm happy to add 2 more to my collection!