It's fine - I had two when I went to a concert last week and wouldn't be able to take anything else in, as no food and drink allowed! I hid the bar. Although they were the mint choc, which has about the same carbs as the shakes. Not sure about the chewy bars, which have more carbs.
The official line from my CDC was along as one of the bars is either mint/peanut/cranberry you will be ok. I know people who do it everyday day without coming outof ketosis just stick to the crisps bars x