The thing about Brumbies is they aren't bred - They breed. Big difference. They are tough, sturdy little ponies but it is pot luck wether they will be good or not - Conformation and temperament isn't something that goes into breeding them, as opposed to purpose bred horses. For a stud prospect I would say a big N-O.
There was one at EquineX on the weekend, but no, I don't personally know anyone who has one. I did meet a beautiful Morgan stallion in America at the barn we rode at - He was amazing. DJJJ Ebony Gold - TaylorMade Stables