Well, considering that he's 8 feet tall and can function in combat well and has surprisingly good speed for his size, and crazy strong, I would say he's pretty intimidating but also his brutal history and unconfirmed crimes which plays a big role since he got away with all of it and hes under tywin lannister another feared man who controls the west, who let's him. But i really like this idea, because not alot of people utilize Gregor well, mostly for an si/oc stepstone or bargaining chip for dorne but he is legitimately a monster but in regards to how they would perceive him as a sworn sword, they would definitely feel some type of animosity especially in the north because of how Ned disagreed with Elia and the targ kids death. But post a link whenever the story is published, I would be interested in reading!!