My dad has one. A beautiful brindle coat. He is fantastic with my daughters! Give him a good belly scratch and you're friends for life!!
Dad says he is more alert to strangers when the grandchildren are around.
I found this on Google. It indicates all the traits "Cujo" displays. I really like these dogs for a family pet!

.366torgue,
I have never heard of an American Mastiff prior to your post. Anyways, a great possiblity that I shall have a Bullmastiff/Rottweiler cross come tomorrow. This will be an attempted replacement of beloved Toby, which was American Bulldog cross.