In addition to the allergy warning it would be great to would great to extend the feature to incompatibilities (phosphates / e450 - e452 for example).
Or to go further and add a great feature: deposit your own black and whitelist for ingredients so that the app helps you which product fits to your needs.
In addition, there could be a smart statistic info which could show, which manufacturer tends to use the entries on the blacklist or whitelist in his products.