There are probably a lot of sugars which could potentially knock you out of ketosis in a kit kat bar. However, there are more carbohydrates in some of the bars, which also could knock you out of ketosis depending on how carb sensitive you are.
Nah, sorry but the kit kat isn't a suitable replacement for a Cambridge bar.
For one thing the CD bar has a 3rd of your vits and minerals, also higher protein to help stop you being hungry and the kit kat will bring you out of ketosis and you really wouldn't want that...think hunger pangs, and cravings for other junk.
Kit kats = nice. You can have one a day for the rest of your life after the diet if you want...just not at the mo