Are Black Australorp, Buff Orpington, Barred Rock and Delaware chickens good to raise for meat?
You've been getting good information but I don't know what you mean by "good to raise for meat"? What are your goals? What are you after?
Others have talked about feed to meat conversion. If you buy all their food that could be very important. If you raise most of it or they forage a lot it may be less important.
How will you cook them? Dual purpose take longer to grow to butcher size so you may be restricted in how you cook them. Frying of grilling an older bird is a good way to create shoe leather but a slow moist cooking method can give you an excellent meal.
How important is size to you? Dual purpose will not get as big as the Cornish X or Rangers comparatively. There are only two of us, I can get two meals out of a small pullet. I like the size of a good cockerel but that just means I get left-over chicken for lunch. For many people size is of utmost importance.
You can hatch your own dual purpose. You pretty much have to buy Cornish X or Ranger chicks. There are some threads on here where people have been able to hatch Cornish X or Rangers, usually crossing them with dual purpose, but most people that try that are not very successful. It's not easy.
If you hatch, half will be pullets. What will yo do with them? If you keep them and hatch many you can be overrun with pullets. I eat mine, some people sell theirs. You need to have a plan.
As far as breeds of dual purpose, what you mention comes close to describing my mixes. Mine are not a specific breed but a combination of several hatchery chicken breeds. Before the Cornish X took over the meat market Delaware, New Hampshire, and some strains of White Rock were the main meat breeds in the US, but that was in the 1950's. For over 60 years the hatcheries have not been breeding these for meat. They are still a good choice but so are several other breeds. If you can find a breeder that is breeding a dual purpose chicken for meat and they know what they are doing you can get a better meat bird than a typical hatchery chicken, but they still will not beat a Cornish X or Ranger as a meat bird. They probably won't be real cheap either but the cost for breeding stock could be worth it.
If you pluck you get a prettier carcass with a white or buff bird. They all leave pin feathers behind but you don't see them as much as you would with a darker bird. I skin mine so it's not an issue. They go through juvenile molts, they outgrow their feathers and have to replace them. If you time your butchering when they are molting and you pluck you can get a real ugly carcass.
We all have different tastes. When cockerels go through puberty the hormones adds flavor and texture to the meat. The texture is why you might have to use certain cooking methods. Many of us like that flavor but to some it is strong or gamey. How you cook it has an effect, but some people just don't like that flavor, especially if they are used to the "store" chicken, which are Cornish X butchered well before puberty hits.
I used hatchery chicks to start my flock. One of my goals was meat, so I selected the larger cockerels to keep as breeders. In a couple of generations I noticed a difference. It wasn't that the biggest cockerels got real big though they did increase in size a little. The big difference for me was that the smallest cockerels got bigger. I still got a pretty big range of size between smallest and largest, but I eat the smaller ones and keep the biggest one to breed. The increase in size of the smaller ones did me a lot more good than the few "biggest" getting bigger.