Official guidance is no bars for the first two weeks.
This dates back to the original four bars because the carb is higher than the sachets and hence the first 2 weeks is all about dropping people into ketosis for hunger protection and hence having bars means you will be hungry for longer.
The new two bars (Peanut and Cranberry) don't have this problem as the carb is the same but the guidance is still no bars for the first 14 days on the diet.
I have 1 cranberry bar a day and this is my first week. I did cd last year though so know from experience that Im lucky enough they dont effect my ketosis or weight loss. But as Mike says really its supposed to be no bars for first 2 weeks.