I have a 3 year old female Cane Corso and we are fostering a 2 year old male Corso for the rescue we got ours from. They are wonderful dogs. Both are great with people and kids, as well as other dogs.
They are protective, but very discerning. If we are out and about they will be super social, but at home or in the car they will bark if someone comes too close. They do not go after anything but will sit and low bark as a "stay where you are." If I or someone they know and trust greets the incoming person and says its okay, both dogs immediately become socal and go up tail wagging to meet the guest. However,I have no doubt that if we were in danger, both dogs would put their lives one line to protect us.
Since you have mastiff experience you will love the breed. Socialize the dog a lot, particularly at home and from inside the car so they learn to not be overly territorial. Working Corsos bond with their flock and the herding dogs/ranchers so they are very affectionate and very good about discerning who is okay (with the owner's okay) but are loyal and protective when they need to be.
They tend to bond more closely to a person of the opposite sex and children who play with and train them. Our female is super attached to me and the male is super attached to my gf, and they both adore our 11yo daughter.
The only social concern i have ever had, and I'm sure you have had the same concern with a Bull Mastiff, is them playing with smaller dogs. Not an aggressive issue, but their size makes them capable of serious accidental damage if they play a little rough with a much smaller dog. A yorkie wandered up by my two playing with another corso at the dog park and I was afraid the little dog would get stepped on or the dogs would tackle each other and fall on her.
Be aware both dogs absolutely are no good with cats or small animals like rabbits. They see them as food. Raising from a puppy might curb that but we adopted ours as an adult and couldn't break her on it.
They chew like crazy so have tons and tons of chew toys around. They drool right after drinking or panting but they dont slobber all the time. We keep hand towels in the arms of all the living room furniture and wipe their mouths after we hear them at the water bowl. We use the command "napkin" and while they hate it, they allow it