They are the quietest, most unobtrusive animals on the farm. Horses are not trustable or untrustable just because of their heritage. The line is not that clear and defined. I have a saddlebred filly I got from a friend that was twice as hard to tame and handle as three of the mustangs. They rarely play horsey games with me just to see if they can get away with a bite or a kick or ignore my requests.
Mustangs can make wonderful horses to own and great companions to have around.