I always ask myself, what's the value of that particular ingredient in the recipe. If it's needed for the acidic quality, then cider vinegar would be good, I'd think. If it's for the taste, then finding a very good quality lemon flavoring/essence that clearly has no lemon or citric acid in it would be a useful ingredient, but certainly not necessary. Better to be safe than sorry, if the ingredients in a flavoring are unclear, and forget using it.
ViolaB