The angled lever on a Miller platform did not operate the brakes, it pulled the couplers apart. A Miller hook operated much like a horn hook coupler on our old HO train sets. It was spring loaded to hold together, you pulled the lever to uncouple. Much like our horn hook couplers, the Millers worked better in theory than practice. They tended to false uncouple, and sometimes jam when trying to uncouple. The Janney was a much better coupler.
Miller also made what they called a "safety platform" that didn't neccesarily have Miller hooks. Miller hooks satisfied ICC automatic coupler requirements, the Janney knuckle coupler replaced them as it became standard on most roads.
Freight cars were also equipped with Miller hooks. Check out pictures of the original B&B two foot gauge equipment that went to the Sandy River.
brian b