Capparelli,
The Maine-Anjou breed became official between the Maine and Anjou river valleys of France in 1909. The first Maine-Anjou cattle in North America were imported into Canada in 1969. The original Fullblood Maine-Anjou were Red and White, with a white triangle on the forehead. These cattle were used as a dual purpose breed, with the cows used for milk production, and the bulls fed for market. Many farms used every other cow to raise two calves, and milk the other. So, to answer your question; Yes, Fullblood Maine-Anjou cattle are very good milking cows.
The American Maine-Anjou Association recognizes Purebred cattle as those registered above 75%. Most of these are now black, containing as little as 1/32 Angus genetics. Maintainer cattle are those registered 25% to 62.5%.
The Who Made Who heifers you are considering could be as little as 25% Maine-Anjou, assuming they are registered. Many Who heifers have become tremendous cows, many horrendous, and most somewhere in between.
To question is good. Please consider the Breeder of these calves. Does he have some history? Is he regarded by others as reputable? Question him about the genetic background of these Who Made Who heifers. If there are more than 3 breeds in the genetic make-up of the heifers, or if he cannot give you registration identification, I would stay clear of the heifers. They might be just too much of a mess.