If you have a milk allergy, using A2 milk won't make any difference, as its still a caesin protein.

The main difference between A1 and A2 milk is that when its digested, the caesin protein chain breaks at a different point and forms different compounds during digestion.

Most of the cows used in our dairy farming are A1 cows. I can't remember the exact percentages, but about 10% of our normal dairy cows are A2. In herds of A2 cows, they genetically test the cows to make sure they are certified A2.

Yes This is along the lines of what I was going to say too. My DS's Allergist has strong opinions about A2 being offered to kids with Dairy Allergies etc and says that it is "such a gimmick" (his words not mine). Granted that it may work in some conditions, it generally will not be helpful at all to kids with Dairy allergies.