I ran a small squad of them, with an exarch, in a winter league. They impressed the hell out of me, just deploy them centrally in cover and watch any space marine player freak out. Teamed up with a farseer, the Duke and the dukes chosen homies, they can give you some control over the middle of the board, and make it easier to flank with everything else, while your opponent is trying to grab cover behind all of his wrecked vehicles:)