Hi, Im not sure if this will help but I used to have a Bullmastiff, I lost her about 5 years ago now and still miss her dearly anyway......
Bullmastiffs are fantastic dogs to have as long as you dont mind the slobber, them thinking that they are lapdogs and laying on you for a cuddle, they love to be around people, they are a little shy at first around strangers but as long as you intorduce them to people and other animals at a young age they will be fine, I have never heard of a "bad" bullmastiff but personally its the owners of dogs NOT the dogs themselves that are bad, but thats a different subject on ere ...
Yes they do eat a lot but if you buy complete food in large sacks its quite affordable, just because you buy a large breed doesnt mean to say that you have to feed it masses amounts of food as you will end up with an overweight and unhappy pooch.
However, Bullmastiffs are notorious for not liking exercise so this breed is ideal for the lazy dog owner lol they are not too keen at all on water either.
Hope you do well in your doggie choice.