This is what the atkins.com site says:

"The Atkins shakes weigh in with 20 grams of high-quality protein, 2 to 4 grams of fiber, only 1 to 2 grams of net carbs and nary a drop of high-fructose corn syrup or other added sugars or any trans fatty acids—and all with 170 calories."

If that is accurate, the carbs should have no negative impact at the beginning. As you progress and lose fat be suspicious of all processed food if you stop losing.

That's my 2cents worth.