I am not impressed with most "dual purpose" breeds of animals. They are breeds that provide both milk and meat, or eggs and meat, or fiber and meat. They can either be hybridized breeds which are a result of crossbreeding dairy and meat animals together or they can be heritage breeds which have been repurposed as supposed super animals who are the best of both worlds. My experience with dual purpose animals is that they are a waste of time and money because instead of getting an animal that performs both duties well, they actually produce poorly on both accounts.
The major problem is that by trying to combine both functions into one animal, you wind up sacrificing their production of both milk and meat. A high production dairy goat is a well made machine who has been bred for generations to take inputs of grain and hay and turn those into milk. A good dairy goat is expected to produce more milk than her kids have capacity to consume. This leaves milk left over for the farmer to have. Dairy goats are not very successful meat animals because the calories which would be used to produce meat are instead converted into milk. Meat goats are the opposite. They are bred for generations to turn calories into muscle and not into milk. They produce milk too, but they only make enough milk for their kids. It is a large disadvantage for a meat goat to overproduce milk because milk left in the udder is an invitation for mastitis.
It is a tough job to create an animal which can efficiently convert calories into both milk and meat. The demands of milk production and the demands of meat production are opposed to each other. A goat can only consume so many calories per day so they can either produce one thing in large amounts or both things in much smaller amounts.
A major problem with dual purpose breeds is this calorie conversion inefficiency. You lose all of your profit margin when you have to add extra calories to an animal in order to get the same production from it as another animal. You could get 1 gallon of milk a day from a dual purpose goat but you would have to feed it a very specialized high concentrate diet and the goat would probably not be producing any meat at this point.
You also lose all of your profit whenever you have to keep an animal of one breed longer than an animal of another breed. Because dual purpose animals are typically for meat and some other product, it generally takes them a lot longer to produce the same amount of meat as a strict meat-only breed. If you have to feed and care for a dual purpose animal one and a half times longer than a meat animal, there won't be any money left over after selling the meat to justify the extra costs.
If you are trying to produce milk, eggs or meat for sale, you should probably pick single purpose breeds that are well-suited for your location and facilities. Even if you are just producing milk, eggs, or meat for your own family, single purpose animals are still the best way to go. You will still have to feed, care for, and breed dual purpose animals just as much as single purpose animals. The advantage comes when you can quickly and efficiently gain products from your single purpose animals. Dual purpose animals are neither quick or efficient.