I have one. Female flashy brindle. Natural ears, tail was already cropped. About 65 lbs.
Not sure about being highly-strung, but they have almost limitless energy and are very physical dogs. They are personable dogs but look pretty imposing because of their "bully" features and big dog attitude.
Mine is a very dominant female. She does not get along with other animals but is great with people. (But not all are like that - some are great with other dogs, various pets, etc.) She always wants to be where I am. She's amazing with kids too - loves them and puts up with all sorts of stuff from them.
They are pretty intelligent and if I'd done more training with her, I'm sure I would think they were even more intelligent. They do have a typically shorter life-span than many breeds. My vet said 8 - 10 years is the average.