As some have sais here, it it manily a question of the ingredients in any processed foods that determine which phase of Atkins it is suitable for.
So if you like a shake make one with no milk/nuts/berries/soy/ etc in it and you will be sticking to the rules
Likewise this is why the bars in my opinion cannot possibly be induction-legal unless you can find some with no OWL rung ingredients in them.
Again you can make your own bars using legal ingredients - I sometimes make pumpkin bars for taking with me.