I think there might be a slight problem here. I'm sure like myself, you have thought that the idea of eating a Kit Kat bar that was flavoured with "Apple Vinegar" might be a great adventure, or at the very least a horrible tragedy you could read about on this site. The problem is I think the use of the word "Vinegar" on this package may have been incorrect. I say this for two reasons. First of all, for the most part Apple Vinegar is used as a cooking agent and very rarely used just to flavour. Secondly these tastes more like apple cider than apple vinegar. So, it leads me to think that somewhere someone might have either made a mistake, or a failed marketing move.
So basically, if you manage to get your hands on one of these gems you're not going to be going for the sour trip of your life. Instead you'll be eating chocolate that kind of tastes like a slightly sour apple lollypop. To me that flavour indicates an apple juice or cider flavour rather than vinegar. I'm no vinegar expert, except for the fact that I love the stuff on my French fries and onion rings, so I can't explain the flavour that vinegar has and that this bar lacks.
I should also mention that I'm not a big fan of sour apple and mixing it in this chocolate wafer format doesn't do either candy medium any justice. So, if you really want to go out and try one of these Apple Vinegar Kit Kat bars you’ll be fine, but if you see something better along the way, go for it instead.